They were competing in completely different environments. (PS2 and Wii) I think that the PS2 would have sold a lot less, but would have still been on top. The Wii would have been a decent second and the Xbox would have sold just as much. The PS2 would still have sold because of the DVD player and the Wii would have sold well to a market that didn't want any video game console originally. I'd say:
PS2: 120m
Wii: 100m
XB: 20m







