"Killing enemies and finding items is a lot of fun, and we think we have a lot of the systems surrounding that right, or at least on the right path with a few corrections and tweaks," Bashiok writes. "But honestly Diablo 3 is not World of Warcraft. We aren't going to be able to pump out tons of new systems and content every couple months. There needs to be something else that keeps people engaged, and we know it's not there right now."
Blizzard is working on version 1.0.4, which will have "as many fixes and changes" as it can pack into one update, and 1.1, which will introduce PvP arenas. These updates will help, as will the progression systems Blizzard is considering, but they aren't the solution in the long run – and since 1.1 is still "a ways out," it is the long run.
"I think both those patches will do a lot to give people things to do, and get them excited about playing, but they're not going to be a real end-game solution, at least not what we would expect out of a proper end-game," Bashiok says.
Blizzard didn't release an unfinished game; it truly believed the item hunt would be a sustainable system, Bashiok writes.
"Hindsight is 20/20 I suppose, but we believed pre-release that the item hunt would be far more sustainable, and would work to be a proper end-game for quite a while," he says. "That didn't turn out to be true, and we recognize that."