http://wii.ign.com/articles/847/847472p1.html
NPD data shows that in December Wii had the largest attach rate of all consoles, which is quite an achievement considering the killer-apps on the other consoles.
Wii: 8.1
360: 7.7
PS3 5.0
As for overall attach rates I think you must compare the first year of 360 with the first year of PSWii. I think they will all be very close.