Federal Government Recognizes Gay Marriage Despite State Laws to Contrary

Crippled though it may be, I thought the Defense of Marriage Act (DOMA) signed by President Clinton was still in effect; so I was surprised to read in the 2014 tax instructions that the Federal government recognizes gay marriage even if your state does not.

Same-sex marriage. For federal tax purposes, individuals of the same sex are considered married if they were lawfully married in a state (or foreign country) whose laws authorize the marriage of two individuals of the same sex, even if the state (or foreign country) in which they now live does not recognize same-sex marriage. Form 1040 Instructions pages 12 – 13

The US Supreme Court has not issued such a ruling. Is this another Executive Order from Obama? I’m surprised there is no pushback from defenders of traditional marriage. Also, where is Congress on this issue?