I can't imagine any other president, in addition to pushing for the many advances the LGBT community has seen over the last three years and advocating for same sex marriage, also devoting an ad to it. You know the Republicans are going to use this for fundraising fodder among the religious extremists. I'm sure the President knows that as well, and decided to run the ad anyway. Just because President Obama doesn't rant and scream like the extremists of the left or right doesn't mean he hasn't been a forceful advocate for people like us.
To paraphrase Harry Truman: Any LGBT person who votes for Romney should go to Hell.