There's always something like this in the works. Over the course of the a console's life there will likely be at least a half dozen revisions tweaking the hardware slightly. Check Wikipedia to see how many versions of the PS2 there were.

Consoles are sold at a loss, and they bank on manufacturing refinements eventually making it cheaper. Odds are Microsoft has at least one or two more further refinements in the works. I believe the 360 and PS3 were based on a 10 year lifecycle, and we're about half way through that now. And that lifecycle might well be extended with Natal and Move just being adapted to current systems.