The only thing that keep people playing atm is because they can smell money, besides that it's a normal singleplayer game that actually lasted quite a few hours for me (and probably alot of people). We shouldn't threat it like a MMO and say it doesn't keep standing, it's not meant to be kept standing.
Initial sales + cuts from RMAH is already a shitload of money from D3 for Blizz. Success for everybody, don't deny you hadn't had fun the first couple of hours/days you were playing the brand new game a month ago.