Before I start, I'm sure you'll think, "Of course Ps3-sales would say that, he is Sony biased". 

With that out of the way, let me explain my unbiased opinion. 

Mario Kart Wii is currently at a comfortable 32.66 million units. Let that sink it for a bit. 
I've put a good 30 hours in the Wii version of MK (hundreds of hours into MK64/SNES) and my overall impression was, is this game innovating at all??? It was released in 2008. That's 3 years after the 360, and 2 after the Ps3 and Wii. Sony and Microsoft had already gotten their online communities thriving while Nintendo really had nobody playing online at all on a consistant basis. Say all you want but I doubt many were willing to deal with friend codes. 

With that said, how is MKWii different from others in the series? I don't get it.

What I do get, is how it could still sell a good amount. It is a very accesible and fun game to play. Very enjoyable with friends. I'm not going to get into graphics.... but you get the idea, there are many positives about the game. 

But COME ON. 32.66 million? MILLIONZ??? Maybe the Wii just has that many casuals in the young crowd picking up Mario Kart. Other than that, 33 million and counting completely boggles my mind. 

Why does it need to be different from others in the series? I don't want Mario Kart to change. I just want new tracks.

Mario Kart, Halo, Zelda, Uncharted, etc. These are all games with a very specific style and their own brand of gameplay. If any of these games changed they would cease to be what we all love about them.

Mario Kart Wii deserves it sales because people bought all those pack in bundles because they WANTED to play Mario Kart with a Wiimote wheel.

you're questioning why a game on the wii had higher sales than a game on the gamecube?

That should answer your question.

1) its easily a top10 game on the Wii
2) its incredibly fun with friends locally or online and you can play others without FCs
3) it was a bundled game for awhile (short stints I think)
4) its the best racing game on the Wii (or anything else AFAIK)
5) it adds new tracks and better boost mechanics than other MK games
6) your mom would love it

I don't get it? You are saying its a great awesome fun game and you are asking it why it sold that well?

Well that's easy.. It was bundled with that plastic wii wheel... I know lots of people who wanted that wii wheel..

It's called bundling.  It works quite well, I hear.

Having read your post all the way through, and carefully analyzed it, I conclude that

Of course Ps3-sales would say that, he is Sony biased.

ill admit i am quite salty about MK getting those sales when modnation racers deserves much more but what can yah do xD

That's what I'm saying. It's a shame knowing that Nintendo hogs all of the casual crowd away from Microsoft and Sony. :(