Though American social laws are often significantly more conservative than in other developed countries, this issue is a bit more progressive.
Proponents of equal rights for gay Americans seemed to generally greet President Barack Obama's endorsement of same-sex marriage rights with one of two responses: great news or about time. After all, if it's the right thing to do, why wait? And why decline to make it a federal issue, leaving the decision to individual states? Why not do more, and do it sooner?
The U.S. is, famously, more socially conservative than much of the developed world. Until Congress repealed "Don't Ask, Don't Tell" in September, the U.S. was almost entirely alone, outside of Africa, the Muslim world, and China, in banning gays from the military. America's continued use of the death penalty puts it in a relatively small club, one heavily populated by dictatorships, war zones, and Muslim-majority countries. The U.S. has the highest rate of prisoners per capita of any country in the world.
So, it would follow that U.S. same-sex marriage rights would be similarly conservative. This is, after all, how we're accustomed to thinking of American social politics: a standard narrative in which Europe adopts some progressive new legislation, then the rest of the developed world follows, and the U.S. Congress finally passes its own version right just as Latin America's implementation rate nears 75 or so percent. But it turns out that this is one issue where, so far, the U.S. is more progressive than usual.