Interesting (and potentially valid) view - I don't think anew Halo or driving title would be able to use Natal fully - but it could provide enhancement. Take driving, sitting for extended playtime holding nothing but thin air is going to be very painful for your arms - any driving title with no controller at all would need to be geared around very short driving sessions IMHO.
MS would be better focusing on totally different genres that truly exploit Natal - and using it to augment other genres where sensible.
In the end I think the challenge with your idea is that many 360 owners, going by Live charts, are playing a heck of a lot on a small number of core titles which do not require Natal at all to enhance the experience.
Try to be reasonable... its easier than you think...
