This being Blizzard, I'm a little more inclined to give them the benefit of the doubt and believe it just might not be for draconian DRM reasons, and actually be for the reasons they stated. Compared to many other game companies, they seem to be all about the online experience.
It seems sort of silly from a user experience point of view. If you start playing online and then for some reason you can't, you have to start over at the beginning of the game. There's no continuity between your gameplay sessions in that case. And that's really how it has to be if you go with that idea; the alternative is too open to abuse.
