I believe that sales for GTA will be massive, I just question if it will boost sales like everybody seems to think they will.
I think that PS3 and the 360 will both sell about 300,000. I predict the Wii will sell 500,000. So the Wii beats the other two individually, but not combined.
I know you didn't ask, but I'll throw this out to: GTA4 sells more on each platform individually than Mario Kart Wii sells.