Chinese food in the US is fairly diverse (and has been for a while). Hunan food is, IIRC, quite common in New York and accounts for most of what New Yorkers think of when they conjure up images of Chinese food. Even in SF, places like Henry's Hunan have been around for a while (early 70s). If you go to the LA area you'll find a large proliferation of Taiwanese restaurants (which are relatively scarce in SF).