Two things. The first is, I don't think the intro really detracted from sales. I think that's a bit of a stretch to say that, "The intro was bad and that's why the game was a failure." There have been several games with far worse intros (and I really didn't think Super Mario Galaxy's intro was bad at all) that have succeeded in sales. You've written a review for the game, and that's fine, but that kind of speculation is making a really big leap that we can't conclude if it's true or not.
Second, you've neglected to mention how LONG it took the previous two games to achieve those sales. Super Mario 64 and Super Mario Sunshine were selling throughout their entire console's lives. At this point we can't say that Super Mario Galaxy won't hit the 10 million mark. I know you have an OPINION on whether or not it will, but since we can't see into the future there's no way we can know what the final sales records for Super Mario Galaxy will be.
What if it does hit that mark? Super Mario 64 may have sold 11 million copies but remember that it had five years to get there before Nintendo stopped production of the game. Super Mario Galaxy is still selling. It's possible that it COULD hit the 10 million mark before the Wii's life span is over.
Lastly... who are we to judge whether or not this game is a success or failure? I don't think it's lack of living up to the sales of its predecessors are really enough to judge whether or not a game is a success or failure. If that's so, then several good games would be considered a failure.
We can speculate as to why the sales are lower, but I highly doubt much of it has to do with the game itself. The reception of it from both gamers and critics alike has been far warmer than what Super Mario Sunshine or Super Mario 64 received. The only speculation I can give is that times change. Those who were interested in Super Mario 64 and grew up with Mario could've potentially grown out of Mario or become disinterested in it. We can talk about casual gamers all we want, but I actually don't know that many casual gamers who actually picked up Super Mario Galaxy. So there's little to speculate there. But the world of gaming has really changed and so has the audience of those games. Some people might've grown out of Mario, others simply may not have been able to get a hold of it yet. Your write up also seems to suggest that Super Mario Galaxy didn't sell as well as the other two because it wasn't as good. Again, a hard thing to really believe given that the reception by many was much warmer for Super Mario Galaxy than either of the previous two.
Don't forget about the competition either. Again, times change. Remember, Super Mario 64 came out for the N64 and for the longest time it was the ONLY quality game you could find on the system. People flocked to it because for a bit there was literally nothing else on the system to the play. It also didn't have much to compete with. When Super Mario Galaxy came out consider it had to do battle with games like Halo 3 and Call of Duty Modern Warfare 2. People might've flocked to say... Call of Duty instead of Super Mario Galaxy... but might've still played and enjoyed Mario Galaxy just fine without ever actually buying it. Not to mention there were quite a few games on the Wii itself. The Legend of Zelda: Twilight Princess was still selling at that point... Metroid Prime 3 dropped down and Pokemon Diamond and Pearl had a sales increase due to the holiday season. When Super Mario Galaxy came out... there were a ton of games it was competing against. Super Mario 64 didn't have a lot of competition at the time it came out, and until the release of games later on for the system there just wasn't that much else people could turn to on the Nintendo 64... where as with the Wii there were actually quite a few games out. Also keep in mind that Super Mario 64 was very new and innovative for its time... and people always flock to new innovations.
What I'm simply saying is simple:
1. We can't determine how many copies Super Mario Galaxy WILL sell. You're comparing its current sales to two games that have been out for far longer and had more time to acquire all the sales they garnered before Nintendo stopped producing the game. Super Mario Galaxy has just now been out for two years. Those 11 million copies Super Mario 64 sold were built up over time. The same goes for Super Mario Sunshine. When Super Mario Galaxy has been out for five years then we can revisit and accurately compare. You have to at least let Super Mario Galaxy have a chance
2. We are not the ones who can determine whether or not Super Mario Galaxy is a success. Only Nintendo can.
3. The times have changed. We can speculate all we want as to why Super Mario Galaxy didn't have quite as big of a success with the Wii base, but even then we're looking at a much more diverse audience where as with the N64 and Gamecube had a fairly predictable and straightforward audience... with the Wii you're dealing with an audience where the majority of its owners may not even care for Super Mario Galaxy (many Wii owners I've talked to over time are not that big on single player games). Nevertheless, there are factors involved that we know little or nothing about at all. We can speculate, but it's a little hard to put our finger on just what happened here because in truth we don't know.
4. A game's quality isn't exclusive to the sales of that game. It doesn't matter if Super Mario 64 or Sunshine was better or anything like that. Did Super Mario 64 sell better because it was a "better" game. We don't know that. Again, there are many factors to consider that we know little or nothing about at all. Look at how gaming has changed and how people gravitate toward what they gravitate to. One does not have to own the game to appreciate it, for example... the majority of games I've conquered this generation are games I never had to buy to conquer. So it's possible that good games won't always sell incredibly well. Why is this? We don't fully know.
5. You wrote a review... and unfortunately not everyone is going to think exactly what you did when it came to Galaxy. Once the game started going I rarely felt it slow down, for example. The exchanges with Rosalie (save for the beginning) were, for the most part swift and simple. Remember, Super Mario 64 also had a slow start. Maybe the intro wasn't as long but again... consider that during that time most games didn't do "long" intro type stuff (and really, Super Mario Galaxy's intro didn't feel that long to me at all). Also, Super Mario 64 did have a sort of sluggish start because for a short time you had to go into the same paintings over and over again before one could truly appreciate just how HUGE the game really was in the end. You're nitpicking at things that don't factor into the game's sales so much as they factor into your own enjoyment of the game in and of itself. If the intro really detracted from the games sales that strongly... don't you think there'd be more word of mouth about how long the game takes to really get going? And as such... don't you think the game might've sold even less?
Being a gamer is about getting your hands on any damn game you can find and playing the hell out of it! It means experiencing the good, the bad and the ugly. It means playing the 360, the Wii and PS3. It's not about that Hardcore and Casual bullshit, it's about your passion for the medium itself!