According to game director Jay Wilson, "As we’re counting down the days until we’re ready to announce a release date for Diablo III, we’ve come to realize that the PVP game and systems aren’t yet living up to our standards. Today, we wanted to let you know that we’ve made the difficult decision to hold back the PVP Arena system and release it in a patch following the game’s launch."
"After a lot of consideration and discussion, we ultimately felt that delaying the whole game purely for PVP would just be punishing to everyone who’s waiting to enjoy the campaign and core solo/co-op content, all of which is just about complete," Wilson added.
He did not reveal when the PvP would be patched into the game, but when it does, Wilson promises that it will come with "multiple arena maps with themed locations and layouts, PVP-centric achievements, and a matchmaking system," and a "personal progression system." He also promised additional updates to the multiplayer portion of the game post-launch.
It seems like Diablo III will be released soon, since Blizzard is admitting that a major portion of the game is incomplete and isn't being fixed before the game launches.
Wilson also emphasized that Blizzard will be focusing its post-launch efforts on finishing the multiplayer element of the game.
A recent rumor claimed that Diablo III will be released on the 17th April.