Some people can grow, some consider the role of the chief executive of the state and the federal governments to be different. Perhaps you are the same you were years ago, perhaps you think Obama as community organizer spoke the same as Obama as POTUS.
I'm not disputing the fact the fact that people can genuinely have a change of heart, but at least you're willing to concede that Romney did change his positions from those he had when he was the Governor of Massachusetts. Some folks won't even acknowledge that much.
By the way, my hunch is that Obama was always pro-gay rights but he just lacked the political courage to say so until he felt that it was safe to do so. On this issue, he's no better than Romney IMO.