I agree with you on your reasoning, but consider this...
The decision of the Supreme Judithal Circus of Massachusetts will be used as the foundation for a lawsuit - probably quite soon - on the Defense of Marriage Act.
I predict the suit will go along these lines:
The Full Faith and Credit clause of the Constitution grants Congress the authority to determine the manner in which the public Acts, records and judicial activities of one state may be proven to occur to the satisfaction of all of the other states, but that there is NOTHING in the Full Faith and Credit clause that allows Congress to opt out of this recognition on the behalf of itself or any other state.
The liberal swine have kicked in the door to obliterating marriage.
It's coming.
We need the Constitutional Amendment to stop it. I think it may be the only way.