In this day and age in which Political Correctness is a protocol of overcompensation for social and political inequities, it's more common to find a racially mixed group of pals in the movies than it is to find a single race represented. If we look at your example of Friends, aren't all of them white? I didn't watch the program, so I can't speak to who they are or who the guest stars might have been who appeared in various episodes. Does that make Friends the exception to the PC rule?

There are few countries in the world that can probably make any claims about the high numbers of indigenous people and a lack of minorities in their populations (i.e. pick some period in time before massive colonization or immigration and look at the population, and compare it to today's population census).

When Rowling started writing these stories, is it safe to imagine that she was hoping to have her books published and read by a few children for the life of the book's run? If so, could she write a book that fit a particular niche in a particular nation, and fill that niche happily without too many demands for cultural diversity because she's writing to the population present in her world? Can she have a world view that presumes many races are extant in the audience (as suggested by KateG) and assume that the faces reading her stories will reflect that diversity? What happens when a story hits hyperdrive and explodes beyond the boundaries of that nation and beyond the boundaries of the language in which it was written?

Later on I'll do a search for any scholarly discussions of the Harry Potter series. One has to work to avoid the moniker of "apologist" when giving a postmodern reading to a popular culture series that often receives a formalist reading from some non-academic (or religious fundamentalist) media critics. There is a lot of baggage within any language, and English is one of the largest (if not the largest) languages. There is also a lot of idomatic material within any given language that may not translate well into other languages or even be understood in other English speaking countries. Some of this may be part of what you're seeing or not seeing.

SRS