I also want to point out the game Darkspore, which I own. I'm not sure what the sales of that game were/are, but it is a single player/multiplayer game that requires a constant connection. I never saw anyone complain about that for that game. Probably because its not Diablo 3. Not one person here said, "I'm not buying that game because it requires an constant connection."
Most people who tried it and said they didn't care for the game, or they bought it, but no complaining about the always on connection.