Actually the problem is you just don't want to admit that the situation is far more complex than you are suggesting so I'll break it down for you: 

1) The console is poor selling. How could a game with mass appeal sell poorly? Clearly it doesn't have mass appeal. 
1ii) Also you have completely ignored the fact that Nintendo fans are not just dedicated, but forced into buying 1st party games due to a lack of 3rd party titles. If you've gone and bought a GC/Wii/WiiU, if you want to play games, you are almost forced to buy 1st party due to a lack of 3rd party titles. No other console does this, so this is why the uptake of 1st party titles on Nintendo consoles is so high. Imagine if CoD was the only FPS on the Xbox - if you wanted to play an FPS, you'd be forced to buy CoD.

2) Well, yes, clearly that is self-explanatory...

3) Are you really using a multiplatform game to prove your point...? Well that's a point not proven as gamers have the choice to buy the console that they prefer the most, and therefore the game for said console. Considering the price of the PS3 it explains a lot why people would have chosen the 360 as their preferred console, or just waited for a price drop. As the WiiU has almost no 3rd party games and is the cheapest of the 3 consoles, obviously these reasons do not apply to it.

In short, MK will sell well on the WiiU, but the sales will be exactly the same as we've seen for past 1st party games. Boost for a few weeks, then back down to 40k and lower. The only people interested in MK are Nintendo fans and they are a dwindling bunch as gaming has evolved, yet Nintendo hasn't. 

1) You are denying the antecedent. A game which has several entries selling over 9 million copies has broad appeal. If one entry fails to sell well, this does not prove the opposite. You are not considering other potential factors.

For example:

If it rains, then the grass gets wet.
It is not raining.
Therefore, the grass is not wet.

1ii) Yep, it's pretty scary going to the shops and having the cashier put a gun to your head until you've bought your quota of 1st party Nintendo titles for the day. I've already discussed the options available for racing games, and even kart racers on Nintendo's systems. Mario Kart just sells better.

2) Right back to denying the antecedent. By this logic, all XBOX Original titles had zero mass appeal, as it sold similar to the GC. But you have denied this conclusion, as it somehow only applies to Nintendo systems. Your logic is completely flawed.

Now you are making leaps of logic. 

You've completely ignored what I said about Nintendo not giving their customers the option to shop around for other titles in the same genre and instead have decided to be immature about it. Not cool dude. When you say broad appeal, what you actually mean is "lack of competition & choice". Also, define "broad appeal". I'm talking about the entire Nintendo ecosystem and beyond. You seem to be just looking at sales figures. When Nintendo needs to reach out to a large market, sales suggest it is just reaching out to the same people with every 1st party title they release This cannot be said of Call of Duty and Forza. It is likely that the two games appeal to two different markets. Nintendo games (and this is my main point) appeals to just one market - existing Nintendo fans. Nintendo third party offerings tend to be shovelware. Want to argue differently? Then explain the poor sales of 3rd party titles *oh snap*.

Don't worry though, I'll have even more proof of Nintendo fans buying only Nintendo games when MK is released as I can guarentee the uptake will be very high, but the console still won't sell well.  

You keep skipping past, every time I mention similar titles, but here's a recap for the Wii U's library -  Need For Speed: Most Wanted (arguably the definitive version of the game), Sonic & Sega All-Stars Racing Transformed (an excellent kart racer), and the upcoming Project CARS (for a sim-style racer). There's definitely competition, so that argument is completely bunk.

The lowest-selling Mario Kart title has sold more than the highest-selling Forza title, yet you claim it is the latter with broader appeal?

Your logic is beyond twisted: that the same people are buying Mario Kart titles, therefore it can't have broad appeal. Firstly, this is another case of denying the antecedent, if the series began with a broad appeal, regardless of the change in sales, it would continue to have broad appeal. Secondly, if this were true, then by your own twisted logic, Mario Kart Wii would prove the series' appeal due to the great spike in sales as it reached a wider audience. Thirdly, Forza title sales have remained similar, therefore using your own logic, that series has no broad appeal either.

You can believe, and argue, whatever you want, but at least be consistent.

3 games hardly gives users a choice xD When Nintendo gamers tend to like karters, platformers and basically the stuff Nintendo has been churning out for the last 20 years, there is no competition to that. Also as for project CARS why would anyone play it on the WiiU when it sells itself on this:

"Project CARS is the most authentic, beautiful, intense, and technically-advanced racing game on the planet"

....It's no secret that the WiiU can't hold it's own against the Xbox One or the PS4. So that comes down to the CoD on PS3 point that the console isn't appealing enough for people to purchase it for such a game. The lowest selling MK may have sold well, but hasn't helped the consoles sell has it? And that's what I'm talking about - the fact that a game can sell well on a Nintendo console yet the console can still sell very poorly. 

Guess what used to have broad appeal - fur clothing. So that's your point killed. I'm not just talking about MK though and this is something you fail to grasp. I'm talking about the entire Nintendo ecosystem. Their titles may sell better than a lot of other games, yet their consoles do not. Why is this? Because their consoles do not have broad appeal (other than the Wii) due to the titles on offer. 

Either way I can't wait to see how you explain MK8's high uptake yet still low WiiU sales when it's back to 40k in 4-6 weeks.  

Keep moving the goal posts, you'll get even better at it the more you practice. As I've said several times now, Sonic & Sega All-Stars Racing Transformed is a kart racer. It performed similarly well across Wii U, PS3 and Xbox360 (despite the large difference in install-base) and has had a 1.5 year head-start without Mario Kart for competition (which according to your logic would mean consumers would eat it up like no tomorrow).

As for Project CARS, perhaps because the devs are putting real effort into the Wii U version, and it's the only upcoming sim-racer on the system. But even if we were to entertain your flawed logic, if customers went elsewhere for  Project CARS (or any other racer) then that would mean more competition for Mario Kart, which directly condtradicts your other train of thought. Like I said, be consistent with your arguments, they're all over the place.

A game could still have broad appeal despite the system itself not having it. By denying the antecedent, you fail to consider other alternatives to your conclusion. The home consoles versions of Mario Kart have all had a high tie-ratio which suggest that the game could have been a deciding factor in buying the console. The console itself not being attractive enough outside of Mario Kart could account for good MK sales on a lower selling system. Regardless of whether or not that is correct, it doesn't prove a lack of broad appeal.

Fur clothing? What a ridiculous analogy; when was the last time you heard someone scream "Nintendo is murder"? I understand that you are talking about all Nintendo games, which is where your argument breaks down even further, as none of your logic applies to competitor consoles. Please go on about Forza again, it was very entertaining.

Here's a fun thought; how many copies would Mario Kart 8 need to sell to be considered to have broad appeal in your eyes?

Keep starting your posts with a claim to have spotted a fallacy. The problem is you clearly don't know what your point is. 

I'm saying that Nintendo do not have a broad appeal as I'm looking at the entire gaming market, not just one title and it's sales, which is a laughably simplistic way of viewing a complex market. 

The Xbox 1 has mass appeal. The PS4 has mass appeal. The WiiU does not, because Nintendo does not have mass appeal. 

"OMG BUT X SALES".
Yes, but Nintendo only sell to existing Nintendo fans. They are a small bunch when you consider the large amount of gamers. 

Therefore no matter how "well" MK8 sells, it won't save the console and it'll just be SB for GC all over again. It's Mario, and Mario only appeals to Mario fans. On the grand schemes of things, there just aren't enough of them. The issue is you're getting tied down in pointless details rather than stepping back and seeing the big picture. How can Mario have broad appeal when the console with Mario on barely sells?

Made it just for your thread..

Nope. SSB and Zelda U will also help wii u. And nintendo might have some surprises left. It will give a decent boost. But it wont be able to push wii u above 15 million numbers.