The IRS has (correctly, I believe) ruled that legally-married couples get to file joint returns. All legally-married couples:
All legally married same-sex couples will now be recognized for U.S. federal tax purposes the same way as their heterosexual counterparts, the Obama administration said on Thursday.
As expected after a landmark Supreme Court ruling in June, the U.S. Treasury and Internal Revenue Service said:
“The ruling applies regardless of whether the couple lives in a jurisdiction that recognizes same-sex marriage or a jurisdiction that does not recognize same-sex marriage.”
I believe there was no other possible result under the Internal Revenue Code now that DOMA is dead, but I'm glad that the IRS saw fit to underscore the point.