My experience living in North Carolina, Texas, New York, and California gives me the picture that this is an exaggeration. Imho, the difference is somewhat like that between a northern town near Newcastle and Covent Garden.

Most nations have regional differences in the realm of the US. Yes, a town like Alba in Texas isn't like NYC culturally or physically, but many countries have this difference.

I suspect that of the many that I have lived in or visited, the only ones with apparent uniformity are ones I haven't really seen deeply: Iceland and Norway perhaps.