Hmm, I don't know how much of a hit they're willing to take to introduce natal. I thought the rumours were that it would be about 50$/£/€? If they then dump the price to 99 for example and offer it for 129£ with natal, then that's not only a hit in the normal sales, but a full hit in money with Natal.
I know they want it to succeed, but to take on the full price of the accessory to do so? They're not Sony >_> (luckily for them in that regard)