Let me add yet another spice to the sauce. Romney lost because he was always mild-mannered and defensive. Obama kept fantasizing out loud about all the wonderful things he would accomplish in his second term. The same things he'd previously said he'd do in his first term, but didn't.
Romney had one opportunity after another to hit back hard and he blew it. Not once did he respond on the order of: "Where were you these past 4 years? Why didn't it happen? And as for me, I've already accomplished, as governor of Massachusetts, all that you promised and failed to do. I know I can do it because I've done it."
In short, Romney lost because he's a brilliant executive, but not a politician.