that PvP game and related systems haven't really met Blizzard's quality control standards as the company announced that Diablo III will in fact launch without the PvP Arena system.
The company said that the decision took a lot of discussion and consideration. Blizzard thinks it would simply be "punishing to everyone who’s waiting to enjoy the campaign and core solo/co-op content, all of which is just about complete."
When the PvP arrives, it will feature Arena maps with themed locations, PvP achievements and a matchmaking system. Apparently, there will also be a personal progression system.
The final part of the statement reads:"We know a lot of you are looking forward to PvP, and we’ll be focusing our post-launch efforts on making sure the Arenas are as brutal, bloody, fast-paced, and awesome as we know they can be. In the meantime, we’re in the process of putting the finishing touches on what we think is a truly epic campaign and co-op experience for launch."
You can find the full post on Blizzard's webpage here