Think of it this way: a next gen console game is basically a good (the disc) and a service (the license, along with the baked in online support). In buying the game you buy the good and get access to the service. If you want, legally, you can totally sell the disc, it's yours. You never owned an exclusive right to that service though, at most you have a contract to use it. Microsoft doesn't have to provide that service to anyone it doesn't want to. First sale doctrine has nothing to do with that.
I'm a lawyer. First sale doctrine only applies to physical objects. So you have the right to resell that disc, but Microsoft doesn't have to honor that sale. Likewise you don't have the right to resell your XBLA purchases.