Wii - 70 million
Nintendos first party games move at least 15m consoles. Wii brand and other "non-games" can sell easily some 20 millions. Casual games with affordable prices, free online like Fifa, Madden, etc, move 20 more consoles. Japanese devs focus on Wii sell 5 more. And correct implementation of the Wii-remote in FPS, RTS and action games sell 10 more.
360 - 50 million
Halo 3 and GTA IV sell 10m consoles. Big hardcore games like Mass Effect sell 5m consoles. Multiplat games sell way better in it thanks to the lower price point, and the small differences between them. Give it 10m consoles. Jap RPG support remains in Mistwalker hands after all of other devs stop supporting 360, but that enough helps them sell 1.5 mil in Japan and 1.5 mil extra in the rest of the world. Online gaming lovers purchase it to play game likes Gears, GRAW, and others. 5 million consoles. And about 15 million more because of gamers that want HD graphics at a decent price ( 250- ), which 360 will likely hit in 1.5-2.5 years. In this group are the kids and families.
PS3 - 25 million
Will sell horribly during 07, pick up a bit thanks to FFXIII, MGS4 and GT5. Those games together with their first party games will move 10m. If they fail to drop the price to 300 before the end o 2009, or lose most 3rd party exclusives, then
I expect only 5 m more. If they get close to MS in price, and keep some support, then 10m or more.