Diablo III is one of the biggest releases of the year, so it's no wonder that when console-port rumors surfaced it was the talk of the town. However, despite a seemingly clear confirmation earlier in the year, Blizzard has only strongly considered a port at this point. It turns out that the deciding factor will be whether or not the game would suck to play on a console.
Blizzard COO Paul Sams addressed the rumors of a console version of Diablo III head-on in a recent interview with CVG. He expressed his studio's interest in making a port, but also some caution with how well that dream would translate into reality.
Same with the console; we don't decide up front that we want to make a console product. We just want to make a great game. If the best experience involves a mouse and a keyboard, we'll put it on PC. If it plays better with a controller, that's the route we'd take. If it works on both, and we don't have to make any meaningful alterations or compromises to the experience, we'd make it for both.
If we feel we can have a game on multiple platforms, then we'll do it. We're not afraid to - that's for sure!
TLDR: If a controller doesn't work well with Diablo III, a console version isn't happening.
Truthfully, if any Blizzard game were to make the leap, it'd be from the Diablo series since both Warcraft (including World of Warcraft) and StarCraft simply require way too many inputs. In addition, the entire business is about making money and making a game available on more platforms (especially such a high-profile game) is a great way to drive revenue. With that said, the fast-paced nature of Diablo III might be the greatest barrier for console fans looking to play the game.
So is Diablo III coming to consoles? Nobody can be too sure, but Blizzard are clearly interested in doing it, and as long as Sony and/or Microsoft don't get in the way, it's a serious prospect.