Colleges do the black (and other crazy jerseys) because it helps to stand out when you're recruiting against 120 other schools. Love 'em or hate 'em, the Maryland unis got people talking (and its worked really well for Oregon).
I just think using black is lazy because it played out at this point -- doing a black jersey with accents that are your team colors. I'm glad the Redskins have never stooped to that. It's fine for the Steelers because black is one of their colors, but I NEVER want to see a black jersey with B&G accents. Hideous.
EDIT: And for the record, I'm not that big on the Georgia or Boise St black jerseys either.