Obama got what, about 1/3 of the military vote. It's not like he needs military support for anything. It won't help him carry a single state in 2012. Any military officer who tries to buck him politically will find their career at an end, and rightly so. Any who cannot follow the orders of him as CiC will similarly find their career over. "The military" is not why this is not done yet.
Further, the idea that Obama should "need the military" is shows a very poor way of thinking. The military serves the country, and needs to do as it is ordered, in the best way it can, and not play politics with anything. You do not have to like it, but that is how it is. I did not like everything I had to do when I served either, but that was not an excuse to do as I please.
The military opposed racial integration, but it was time, and it needed to be done, and it was done, and the military today is better for it. This will be much less disruptive to the military than racial integration is, and it is time, and it needs to be done. A few people who cannot adjust to the way of the world will be pissed, but most will just get on with their jobs.