One way or the other, a person will prefer either topping or bottom. Yes, there are versatile people, but most people are one or the other.
Yeah, I really do think that's a cultural thing. I've noticed Americans (not all of them; I know a few exceptions to the rule) are super serious about that, and all the Canadian queer guys I know who've lived in the States for any amount of time have been like "wtf is with this top/bottom shit?" And they report that all their American partners are dumbfounded that they reject being forced into one role or the other.