Don't you think the lack of DRM is percisely why the current d2 bnet is constantly camped by bots ?  We don't know the exact methods of their DRM but perhaps by limiting the content of the game to be stored locally, the hackers will have a harder to time to figure out how to mess up the online experience for everyone else. I understand the grief of having to be online to play offline but let's be realistic, Diablo is no longer a single player first, multi second kind of game. In fact that change took place in D2 and that was 10 years ago. It's the multiplayer aspect of the game that has prolonged its shelf life and it's popularity amongst gamers. Thus, it's only logical that they are doing their utmost to protect the multiplayer content of the game.