No there isn't. Compare married filing jointly with married filing separately. There's a difference, often quite significant. That's the "benefit" the gays are talking about.
Oops. I should have said: compare married filing jointly with 2 singles filing separately.
As I said, with 'two income earners'. The only way married filing jointly comes out ahead, is if all or the vast majority of the income is earned by one person. Two income earners filing as individuals comes out ahead of married filing jointly when all the personal exemptions are taken into account. That was definitely the case a few years back, and I don't think Bush's tax cut fixed that problem.