The difference is... that's digital content.
However, since a game on XB1 is nothing but an install disc, installing a game tied to only one XBL account, once it is banned, all your physical copies are also useless... or so it seems right now.
Steam has physical discs you can purchase, and once they are put in the PC they are required to be linked to your Steam account. If you are banned on Steam, you lose access to that game, even though you still have the disc and all the game data is stored on that disc. So no, it's not different.
Besides, I don't see why digital games should be held to a different standard than physical ones. Games are games, regardless of their distribution; whether you downloaded it or bought a disc, the content of the game is still stored locally, in your hard drive or on your disc. So it's either OK for a service to have this kind of provision in their ToS, or it's not. It doesn't matter if it's Steam or Microsoft who does it; either it's acceptable for both of them, or it's acceptable for neither of them.