There is an American culture. It's not too oblivious to Americans but, oblivious to other people. That's basically saying that England doesn't have an English culture and they are just as diverse as the United States.
What I mean is that so many people bring their culture here that there really isn't any original american culture. All you really have in the "american" culture is just combination of many and there's not really a definition of it.
Oh, and lived in Mexico for a couple of years and that's not how they make hamburgers