"Statian" would be the adjective and common name used instead of "American" to talk about people living in the USA.

After all, Cuban, Panamanian or Brazilian people are also Americans !

Edition (mai, the 22th) : searching for "statian" in Technorati, I found another blog posts where this word is used. These posts were written before this one, of course. This is great to discover another people had the same good idea, even before you.