My black friends. neighbors and coworkers sound basically like their white counterparts.
But every time I see a black “person on the street” interview I hear dialect straight out of Gone With The Wind.
I think they must be bypassing the well spoken blacks to demonstrate they are reaching the “real” black community.
I’ve heard that sort of things happens in casting TV shows and movies, where a mainstream-sounding black isn’t “black enough” to fulfill the duty of being the token black in the cast.
I suspect, black or white, that the more well-spoken you are, the more self-aware you’ll be about the dangers of talking to the media (especialy man-on-the-street bits) and potentially coming off sounding dumb or inarticulate. It’s not like most white people I see in those pieces are able to do more than put a couple feeble sentences together themselves (either because they’re nervous or that’s simply not their communication strength).