@ Kasz216
I think I am correct.
Those who like the XBox for its games are more likely to have upgraded towards a 360 (nomatter if owning a PS2 as well or not) as sequels to nearly all big XBox games have already been released for the 360.
Fans of GameCube games like Mario Kart, Smash Brothers, Zelda, Metroid, etc are also more likely to have bought a Wii. As those sequels are also already out for the Wii.
With regard to the PS3, it's the console with the highest entry pricing. I think many are waiting for the price to drop or for sequels to the PS2's most popular games, like Final Fantasy, Gran Turismo 5, Kingdom Hearts, God of War, Jak & Daxter, team ICO game, etc. I think it's certainly a combination of various factors.
Also note the 360 had a year headstart on the market, so 1 extra year of people upgrading towards this platform.