From the page linked in the OP:
David Popenoe, co-director of the National Marriage Project at Rutgers University has said that the survey doesn't make sense. He based this belief on his assessment that Christians follow biblical models of the family, making a bond that "the secular world doesn't have...It just stands to reason that the bond of religion is protective of marriage, and I believe it is."
Haha, great scholarship there!
Incidentally, Massachusetts has the lowest divorce rate in the US, and also has gay marriage. It'd be really cool if, when enough time has passed for meaningful statistics to be available, it's found that gay marriages result in fewer divorces than straight marriages. Imagine the exploding heads!