@Thomas,
Thomas wrote:
How can the states' right to regulate marriage decide this case when the 'state' who married the couple was a foreign country?
Top of page 3 of the opinion: "The State of New York deems their Ontario marriage to be a valid one." Once New York recognized their foreign marriage, they were legally married for all purposes in that state. It's the same for any other marriage concluded in a foreign jurisdiction, and states routinely recognize those marriages without any fuss. The only problem occurs when a marriage that is legal in a foreign jurisdiction is not recognized in the state, such as when a polygamist immigrant seeks recognition for all of his marriages. That's not an issue in NY, however, since NY permits gay marriage.