Not remotely sour, but you are wrong. Just because a game is designed with multiplayer in mind does not make it a multiplayer game.
I'll concede incorrectness on my prior view before reading this statement, but not on diablo 3; in diablo 2 the multiplayer was fairly broken due to several things, primarily the fact that you could intercept data and create items the server would allow but would never generate naturally, and dupe items.
I suspect you never played diablo 2 for a protracted amount of time
before patch 1.10.
We could argue this out, i wont blatantly "say you are wrong". But I will say that as blizzard released announcements about diablo 3 as it was in development, i was very supportive of the changes.
It is unfortunate that the new cheat protection is read as many as "always on" DRM, that is not its originating function, though im sure it made the activision execs happy.
It is entirely playable in single player, a mode in which you do not have a 'party' of characters to make up for a lack of other players. It's a solo-able game.
As to single player, anyone can play single player any time. (this reads as a correction, sorry)
Offline single player is the big complaint, i agree with all bar one thing blizzard have changed since diablo 2, and it is the lacking of offline SP characters, though for all the people who cry that it would be an easy change, blizzard already stated it would not because they built it from the ground up to be server based, so all the items and enemies are handled by the server. Like an MMO.
The people who cannot play because they to not have access to the internet for whatever reason
should not buy it rather than complain about their entitlement to play an online game they bought offline.