A fairly obvious point you didn't make in your post: I don't think the comparison can ever be made about marriage rates for gay couples in Massachusetts (or any other state that grants gays the right to marry) unless there is full recognition of such marriages on the federal level. Even if I could marry under state law - the lack of federal recognition means the institution for me is still a second class affair. Important tax and other federal benefits are missing.
In my own case, my partner and I are selling my house here in California - and I will have more than $600,000 in gains. We've been together 4 years. If I gifted him half the house - he would be taxed. A couple who could have married however, would get a $500,000 flat excusion for gains under the tax code. As a single, unmarried man I get only a $250,000 exclusion - meaning that I am paying in just this one instance more than $100,000 penalty in taxes that a married couple would not have.
Very painful to think about. Less rights than any straight person - and a heavier tax burden. So much for the guarantee of equal protection under the law.
It should make every American citizen cringe!