don't discount the importance of Godfather: Blackhand edition. I think it's of critical importance for Nintendo that this game outsells the other versions of Godfather, by quite a margin. Nintendo currently has a 2:1 margin over the PS3 Worldwide, and I don't see this increasing by a lot without strong third party support.
Nintendo needs to convince the third parties to create games for their consoles. If Godfather: Blackhand doesn't outsell the PS3 version with a 2:1 margin of consoles, when it is a game that is critically acclaimed, then what chance do other games have? Nintendo already has a reputation of being very difficult for third party developers, generally because third party developers don't put much effort into their games.
It appears EA is (very surprisingly) putting some good effort into creating games for the Wii. If this (and MySims) doesn't pay off for them, then other third party developers are going to find it difficult to justify making games.
Let's not also forget that this game is basically a head to head battle between the two different philosopies, Nintendo's idea of emphasising innovating gameplay over graphics, and Sony's philosophy of being a next gen powerhouse. The PS3 version doesn't even look that good, from what I've heard.
If both this game and MySims fail, then it's going to be difficult for Nintendo to convince third parties to put leading teams developing for the Wii. And without strong third party support, we'll see the same thing happen to the Wii as the Gamecube (well, not quite that bad, but you get the idea)