It makes sense Business wise.
FortressCraft is one of Xbox Arcade's best sellers at the moment, so there is an audience on the Xbox already, plus Xbox live is a better online infrastructure than PSN, and the recent hacks and down time couldn't have done much to sway Notch.
Re: Rpg mode, its good, but if he is adding features like hunger and such, we need more control over turning individual aspects on and off, instead of a choice between adventure mode and creative mode.