Certainly most progressives know that Obama is not the Supreme Court and I doubt that you could find a single prominent progressive that claims otherwise. Posts from a couple random internet posters who most people have never even heard of mean nothing.
And here are some words from your link to Ameriblog:
I was equally troubled by the administration’s explanation that they had no choice but to defend the law. As an attorney and as someone who was directly involved in giving advice on such matters to another president (as a Special Assistant for civil rights to President Bill Clinton), I know that this is untrue.
snip
Thus, the general rule that the DOJ must defend laws against attack is relative – like everything in Washington. And even when the DOJ does defend a law against constitutional attack, it does not have to advance every conceivable argument in doing so (such as the brief’s invocation, in a footnote, of incest and the marriage of children). In fact, many legal experts believe that in this particular case none of the issues going to the merits of whether or not DOMA is constitutional needed to be addressed to get the case thrown out. The administration’s lawyers could have simply argued, for example, that the plaintiff’s had no standing. There was no need to invoke legal theories that were not only offensive on their face, but which could put at risk future legal efforts on behalf of our civil rights.
If you want to dispute that fine, but they are clearly not advocating that Obama break the law outright they are claiming that the DOJ is under no legal obligation to defend DOMA in this manner. Certainly they were under no legal obligation to claim that gay marriage would deprive the federal government of revenue or to compare it to incest.
Arguing against the DOJ case defending DOMA is not suggesting that Obama should be like Bush in any way. Do you know who does want Obama to be like Bush? The ones who tell us that he should allow government officials torture to walk away without prosecution, the ones who tell us that he should continue to monitor people's phone calls without a warrant, the ones that tell us that he should continue to honor anti-gay bigots like Rick Warren. Those are the people who want Obama to be like Bush, not the people who believe that our government should never compare gay marriage to incest.