re: Why does the national media never talk about black on black crime?

I'm guessing it's for the same reason they don't cover white-on-white crime. If you look at neighborhood demographics, the U.S. still exhibits high levels of racial and economic segregation. It makes sense, then, that crime perpetrated by a black person is more likely to affect another black person. It's the same reason why crimes committed by white people are more likely to affect other white people.