The games are the key point. Nintendo didn't win the new audience just by throwing a new controller at them, they sold to that audience by giving them games they wanted and they used a new controller to do so. Technology is an enabler for games that then sell the system, it is not a system seller by itself. I don't think MS or Sony have the capability (mostly based on understanding, those who think the extended market means "casual gamers who have no taste" or "people just like us who just can't handle difficulty and need easier games" will not reach that market) or desire to build a game library that appeals to the extended market. You can't just take a market like that with one gimmick and a token game, you need to commit to it. MS and Sony are focussed entirely on the core market, they would have to split their attention like Nintendo does. There we have the next problem though: How much attention, i.e. development capacity, do they actually have available for splitting? Both MS and Sony rely strongly on third parties, they have very little capacity of their own that could be used to go where third parties won't (and they definitely won't, they're failing to capture the market on a system that already has a huge number of extended market gamers, they would never do it on a system that doesn't have that market at all).
Finally, the crucial bit that made me think Natal is too late was this: During the conference the guy said the dev kits are going out NOW. That means games can only now START development (and since the concept of Natal is just so different from the regular controller I don't think you'll be able to incorporate it into an already running project without turning it into the controller-less equivalent of waggle*). What does that mean for the game releases? They'll be VERY late in the game.
As such I don't think either of the two will make inroads on Nintendo's market, they lack the necessary skill (the software development, not the hardware), the necessary motivation (they'd rather serve people who actually care about graphics and cinematics and HD) and the opportunity (they could have been there to compete with the WMP this year had they revealed their clones last year but now they're going to be late to even that party and when they finally launch go up against an already matured library which is further boosted by the Wii's previous focus on motion controls and thus involving less shoehorning).
*= To me waggle means substituting a digital input with a gesture so the resulting game could have been played just as well with a button, Wii Sports is NOT waggle because its gestures are analog, the way you perform them affects the outcome. Many core games on the Wii use waggle though because they still get designed for buttons.