This. The differences in culture from state to state in the US can be every bit as different as they are from country to country in Europe. I think any writer can have any setting, if the research is there and, if it's contemporary, you include Betas from that area. I had a journalism professor who said "It's 'write what you know,' not 'write what you already know.'" Wise man. I would recommend, to save yourself some headaches, that the narrator be a transplant to America, rather than be an American. There's a formality that often still comes through in the British version of a casual voice, and the flow of the British voice tends to be more clipped and precise than our languid American style. I don't mean one or the other is bad or good; I'm just saying it can be a giveaway. I accidentally outed an American acquaintance who used an English ghost writer for her memoir by blurting out "Is your editor based in London?" Oops.
