It proves the Wii truly deserves the dominance it has. Why release 10 hardcore games which sell 2M at most each when you can release one Mario Kart and sell 20M!
I'd actually rather have MORE games to play, then be happy if HEAVY RAIN were to sell 20 mill or not. But that's another thread. It's good for the game either way.
Less is more?
Why would fans care about a game that sells 20 million, when they could have multiple games with moderate - great sales? Come to think of it, most fans don't care that Mario Kart Wii sold 20 million copies.
I'm not saying that sales don't matter to anybody, as obviously the devs would love them to be high. But why should any GAMER care that this game just crossed 20 million? It was a success before that so 20 million just proves that it's a monstrous success. If there are more games to play with less sales though, I don't see why the majority would care for ONE game that does this. More games = more incentive to buy a said console, thus, the industry continues forward.
The PlayStation 2 wasn't a success story because Gran Turismo 3 A-Spec sold 14mill+. It was because of the plethora of titles that graced the console, which to this day, is the highest in history.