The PS3 did really well with teh slim, it's not often that you will be able to drastically cut down on the manufacturing cost for electronics, and sony made a bigger reduction in the build costs than a normal die shrink would do, so they are living large now.
MS seems to be doing two things right now to add more value-
a. Natal - I think that it's going to go nowhere
b. Price cut- this is where MS has more room, I mean they've made a decent profit for a while now, so they definitely have some room to cut the price. The only reason why dont want to now, is that they will look weak for doing so, most electronics companies dont cut prices right after it already did that. So, MS might want to wait a few months before it does that, to say april or may.