There have been people openly admitting they will pirate the game over this.
Rather amusingly, if pirates are able to negate the need to have that online connection, then I may actually buy it and use their crack. I couldn't care if my characters are stored on Blizzard's online server, nor do I care for using their auction house, but if my rather unreliable ISP cuts out right in the middle of the evening during a session and the game won't let me play any more, then that's something you better believe I'm going to give a damn about.
Just out of curiosity, is it setup where they're going to have server maintenance (like Wow), during which time everyone's going to be unable to play? For your average Yank, that's never been a problem, but out here in Australia that maintenance drops right in the middle of the evening.
Do your shit, pirates, some of us are counting on yas with this one.