Umm, there is very little American cultural diversity. Slight differences in lifestyle don't make for cultural diversity. At least not in comparison to the various countries of Europe.
Agreed. I'm American and spent three months this year full-time travelling the US by car. I did a complete circumnavigation, with a side-trip to Toronto thrown in. It was clear to me that, despite some small regional differences such as accent and general political inclinations, the country is remarkably homogenous. In the States we're far more "informed" - that is to say infected - by the nation-wide "news" media than by regional cultural memory. Texas remembers the Alamo, Vermont remembers Ethan Allen, the Pacific Northwest remembers Lewis and Clark, all in some fairly vague way. But nationally, everybody remembers <insert low-brow TV program name here> from last night and that's something to talk about!
I'm Russian and will argue that most of the eastern Europe has very similar culture. Just because you rotate your head to say yes and nod to say no, does not make it vastly culturally different. The culture curtain ends somewhere around Czech Republic. Yes, I am even willing to say Ukraine is about 99% culturally similar, and that should stand for something since many know how much Russians despise being associated with Ukraine.
I am Ukrainian and I disagree with you strongly, mainly because of your out-of-blueish 99%. Traditional culture is very different. As for an urban one, while Eastern and Southern regions are similar in very aspects to Russia indeed, they are not what we mean by Ukrainian culture at all.
While I am not a researcher by any means into cultural history, I have lived 20 years in Russia, 3 years in Ukraine. I also have a deep Polish background. The differences in the cultures between these 3 is relatively minor.