Now, it's true, GTA has a lot of casuals playing it "to kill hookas", but even so, the type of casuals that had GTA on the PS2 are not the majority of casuals that own a Wii only, at least on the West (In Japan it's different)...
I think 5 million is high, but lets take it, how much millions GTA is selling in PS360? PS3: 5.2M, 360: 6.6M, Total: 11.8M... The game is almost at 12 million being multiplatform, if the Wii sells 5M, this won't be enough to make it exclusive, but it will be more than enough to make it multiplatform (Wii-PS3, 360) which proves my point...
@Naum: I used a FPS because it shows that userbase alone is not enough to predict sales...







