Let's look at it this way. The reality is the Wii's general lack of power, bordering on last gen in general terms means that it is easy to get away with making crappy Wii mote powered games. Infact everything about the Wii is geared towards generally quirky easy to pick up and play games built around using the Wii mote. Those games that have tried to combine serious gaming plus Wii mote action have in general failed to do it very well and that's on the god damn Wii.
Now shift this across to PS3 and 360 and throw in the cost of having to develop fully fledged games on those two console formats. You have a situation were you
a). Create a game purely designed to work with the motion sensing tech, or as it's known try and beat the Wii at the quirky body flailing game. If that's the market you're aiming at why develop for MS or Sony when you could do the job on the Wii at a greatly reduced cost and release it on a format that already has the user base who would be interested in it.
b). Create a game that attempts to combine serious gameplay along with motion sensing nonsense or tackle the market that even the Wii hasn't managed to get right. Well I own several games that use the Sixaxis function and I don't use that function for any of them. It's less accurate and feels retarded. Now multiply that factor to your whole body and attach it to the fact that it's making a game harder and less fluid than it would be if you were just pushing a button and now you have a whole bucket of fail.
Unless MS and Sony have very specific plans to target the market that is actually interested in this kind of thing, i.e the people who already own Wiis I can't see how either of them are gonna do very well with this new jump on the Wii bandwagon approach. To be honest I doubt very many of their current main developers will even consider adding functionality for their new motion sensing tech to their major main line titles, instead we'll get what we saw with the eyetoy. Games that are designed only to use the eyetoy rather than big name titles that seamlessly added eyetoy functionality.