I'd be willing to bet they have server que's day one for people just wanting to play single player.
Playing a single player mode in an online only format is just an illusion of playing a single player mode.
I remember D2 starting off a little rough, but once you got the game activated you could go OFFLINE and not worry about the internets.
This game will definitely have queues the first week or so. Every new MMO (which D3 is technically architected as) has queues for a while. I won't be waiting for any queue to play a SP mode of a game.