It doesn't surprise me this type of confusion when you can have MMO databases
listing Diablo, when people actually try to discuss
if Diablo is an MMO, or even when Diablo 3 is often discussed in terms of, or compared to, existing MMOs (and often on these same forums).
So be gentle on the OP. He's more right than wrong.
This is the answer I was expecting to see when I was reading the replies:
BigKevSexyMan, Diablo 3 is missing just one game feature to be considered a MMO. Diabo 3 will not offer a Persistent World to its players. Worlds are created when you leave the chat window and start a new game. Maximum number of players on each game will be limited to a predetermined number. Currently this is supposed to be four players. Less than the eight players in Diablo 2.
Diablo 3 is thus an Instanced World and doesn't fit, as such, in the MMO category of games.