[...] for me the ability to buy a single copy of a game and share it between all ~5 xbox users I know will be a lot more useful.
My guess is you're reading too much into that feature, that won't be how it is going to work. No more than one person will be able to play a shared game at any given moment, so no multiplayer co-op or combat, and no achievements for anyone but the owner, scrap that, the licensee, plus a lot more of similarly arbitrary restrictions.
My mother is a fish. - William Faulkner