I'd say it's more like it failed because Blizzard entertainment was trying to make a game for a genre they know nothing about.
EDIT-- But then again, the WarCraft franchise was an isometric strategy game prior to World of WarCrap, and WoW is both first and third person, so, like I said, it's not like they don't step into different perspectives and view modes. And it's not difficult to program a first-person game, so, there's no reason Diablo III can't be a first-person/third-person RPG, which empowers people to choose between standard, first, or third person.
EDIT EDIT-- What I'm saying at it's essence is, don't get pissy if they add in first-person options for Diablo III. Not everyone likes to click on something and watch a character walk across the screen to kill it. Some of us like to do the walking ourselves.