Well the kinect maybe be better because you have no need of any controllers, you just use your body, but the games they will bring out for it will be far removed from the Wii ones. What I mean is, they won't be relaxing puzzle games and such, but will focus more on family friendly action games, where the whole family has to jump and move around. Which is going to flop, because how many families do you know that have enough time to play games together, not many, most everyone has jobs and are tired.
Also the PS3 Move is said to be more focused on action games as well, with a few for hardcore players, but you need two controllers like the Wii.
So I don't know how useful these new motion controllers will be for the disabled, mainly because the Wii is the one that has a foothold there and the others don't want to be accused of copying it. So for as long as I can see, what the Wii is doing, will most likely be the only stuff done.
Obviously the Kinect and Move will have fitness programs, but thats not the same.