http://games.ign.com/articles/829/829372p1.html
It seems as though the MS strategy is to compete more directly against the wii in the relm of family friendly gaming systems. Might not be a bad plan to have an Arcade version to compete with the wii, and then an advanced version with a built in HD-DVD next year to compete with the PS3 more directly.
I personally think the 360 owes its success to being the middle of the road offering, but that is just me.