That's a good question. More basic, are gay married people allowed to file Married on their 1040? What if they move out of the state to a non-gay-marriage state? Are they automatically divorced? Property rights? Children? Is a gay partner shielded from testifying in court against the other partner if the crime was committed in a non-gay-marriage state? So gay-married people can never safely travel or move to a non-gay state. Can you be gay-married in one state and hetero-married in another?
Marriage is integrated into our civil laws, some state and some federal. How can gay-marriage be a state issue when there are federal implications?