Blue's News points out a few impression pieces that inform that the fourth class will not be appearing at Blizzcon.
More information.There's A Quick Diablo III Recap before Blizzcon on OS X Reality recalling what we've heard about Blizzard's action/RPG sequel. There's also a Blizzard Offices Diablo III Demo Report on Diii.net ahead of this weekend's BlizzCon. They offer extensive hands-on impressions of the game, and share indications that the game's fourth playable probably will not be revealed at BlizzCon as many have anticipated. They describe how the several game functions have evolved since Diablo II, including the inventory, quests, skills, skill trees, the lack of mana orbs, and more.