I guess Nintendo has played around w/ Natal and Sony's prototype before, since they've been messing around motion control for the 5-6 years now, but Nintendo decided to go w/ WiiMotion Plus instead.
Nintendo is the undisputed market leader in motion controls and in the casual gaming market segment. Moreover they have a nearly 5-6 year technology lead on a market with absolutely no competition. When Sony and Microsoft will finally get there, Nintendo will simply move to the next big thing, so no danger there. I do hope that both MS and Sony makes their motion control accurate, cheap, and gain developers support or it's not worth for consumers to support it at all. I wouldn't throw $200+ on Sony or MS add-ons until I see a $h!t load of hardcore games are out for them. How long will those games take to make or are they going to be even made at all? Hopefully by that time, I still play video games.