So your saying the market for the Wii has dried up so MS is only trying to sell the Natal to people that already own a Wii. MS is not going after the people that already purchase a Wii.
They will now be offering a console that does what the Wii does and much more. Some people that havent picked up a Wii yet, but are interested may just change and pick up a 360 with Natal.
If the mainstream media declares the Natal as hot stuff next holiday sales of the Natal will be huge even with people that havent picked up an Xbox 360 yet or maybe wouldnt have.
Sure, "some" people will. Just not very many, as these things go. Natal wont break 300k unit sales next year, unless MS starts packing them with every xbox which they may in fact still do.
The question is what type of game do you really want to play with something like this. The next question is what type of game do you want to play on something like this that hasnt already been done very well on the Wii. Wii already has Wii fit.....
Next thing to consider, is that when you think about it... an actual remote is also much faster and easier to use than Natal for general purpose stuff. The idea of not having to find your remote is a good one, but even most people who get a Natal will liekly end up using their remote most of the time, simply because its a lot quicker to navigate your menu just using your thumb than it is to wave your whole arm around.
Natal tech will pay off in the long run, but I would really like to see someone come up with one attraction outside of novelty to the device in its current iteration. MS and Sony are both doing the "me too" right now, noone has any idea how to utilize it for an FPS or RPG etc that people would really want to get into yet.