They claim it’s for community reasons, they claim it’s to allow savefiles, and they claim it’s nothing to do with piracy but I find most of these statements questionable at best. Blizzard is surprised at the backlash despite a strong foot in the online gaming industry.
Frank Pearce of Blizzard said “I would never say it is not a factor, but it’s definitely not the driving factor. Ultimately, if people want to pirate the game, they’re going to find ways to pirate the game whether we require an online connection or not. Our focus is not on preventing piracy, but rather on creating an online experience that’s so compelling for people that they aren’t thinking about pirating the game because they want to be part of this community and they see value in having this community, almost as if this vibrant community is a bullet point you would put on the back of the box as a feature. The exception will be the games that aren’t connected.”
I honestly spent more time on Singleplayer due to Blizzard’s refusal to create a very simple dynamic and learning spam filter that would solve a lot of problems. They can justify it until they are blue in the face, but mandatory internet for playing on single-player has become taboo in the gaming community and no matter what Blizzard does, the players will always call it DRM.
Someone who pirates the game however will be unable to take advantage of Blizzard’s online services, but I’m sure not many gamers care about server-stored saves or the auction house.