There are core differences. With apps it is
possible. You can't "hunt down games". That is why it only affects apps and not the XBox games. It is a matter of practicality. That is one of the possible dangers of DRM, they can shut down your games. With a retail game you still have property of the medium, so they couldn't just confiscate that. Eg, a german court could order Steam to shut down my copy of Dead Rising 2 (theoratically, and the issue would be very different), yet as long as it's possible, it will be an option.
Additionally, I would guess that apps run under a different license than games. An app is probably a "service" and not a finished package like most games are sold. I honestly haven't looked it up, but from what I've seen so far on my phone that seems to be the case.
Wishbone: Well done, you. Except that you didn't bother to check if it ever actually happened, did you?
Well, the game was pulled before I joined. And I stumbled upon threads like this
http://www.gog.com/en/forum/toca_race_driver_3/we_want_to_download_toca_forever which made me think that game wasn't available anymore.
Edit: And GOG pulled various extra for
exactly the same reason. Probably a dozen soundtracks at least ...