There's going to be extra content that wasn't in the PS2 version. I think the Wii version will be upgraded graphically from the PS2 one. I mean, Manhunt 2 even looks better on the Wii, apparently. And they'll have to upgrade their graphics anyway for the Xbox360 version.
Anyway, some rumours that are slightly related:
- Sounds like Rockstar has *another* Wii game ready. The Warriors? A GTA game?
- Eidos is making a family-oriented game for the Wii (hooray...).
Both rumours come from very credible sources with good track records, so they're very likely to be true.