Most people I ask have noticed and many believe it is some kind of social programming.
I've tried to find some reasonable explanation involving demographics, or sales techniques, anything that could indicate that this type of advertising is effectively selling the product or service advertised.
A first I thought that they were just casting as wide a net as possible, or that they are targeting a specific market in urban areas, or trying to be inclusive by not leaving anyone out, but none of these possibilities pan out for me. They are not representing an accurate minority percentage of the US population, even ignoring larger ethnic groups like Asians and Latinos. Plus, the groups they focus on are not accurately portrayed.
The African American demographic they over represent in advertising is most often presented like they were an upwardly mobile nuclear white family. I'm not saying that black people only live in impoverished slums and have no upward mobility, but it seems like there aren't even a lot of white folks that live like WASPs or Yuppies these days, much less the majority of African American consumers.
So I come to the conclusion that it is some kind of programming directed mostly at whites, but blacks as well, to the exclusion of other minorities.