For quite some time I've said the only thing DRM does is penalize legitimate owners, nowhere has this been proven more than with the release of Diablo 3. Endless people shelling out sixty bucks retail only to be confronted with "error 37" on trying to play, because even in single player you have to remain online.
Net result? While what's actually going on right now is unclear in terms of the how/why, the what is obivous:
So NOBODY can play Diablo 3.... and since battle.net handles all logins for WoW....
Guess what other game is now down due to this mess?
MMO launches are always painful, but when you start having that level of pain on a single player release, to the point it screws up your ENTIRE business and every one of your clients, that takes a special type of ineptitude.
Though I'd not be surprised if it was a DDOS as 'lashback' against the 'online only single player' model.