I don't think that adding the motion control to the 360 will do anything to effect Wii sales in the slightest. In fact, it could end up doing the exact opposite.
By adding a motion control stick to the 360 all M$ does is concede that Nintendo has a better product by imitating what they don't have. If they do the motion controls poorly (which is very likely to happen) like Sony did then their version just looks inferior and people will be turned off by it.
Also as others have said lack of support for the thing will keep it from ever being as popular as it could have been had M$ launched with it.








