I would like to think that he supports gay marriage, but that he recognizes that it's just not politically possible. The vascillating then becomes the balancing act of his cover story -- trying to annoy the least number of people with his dodging.

The other possibility, that he is undecided or has no reasoned position on the biggest civil rights question out there -- I just can't see that being likely.

trying to annoy the least number of people with his dodging.

Sure, but by doing so he's increasing overall annoyance from both sides. As the main link pointed out, his administration can choose not to defend the current law or at least not so vigorously. I suppose he's trying to keep the issue on the back boiler since he definitely doesn't want to address it before health care reform, but he's doing a pretty clumsy job of trying to appease everyone.