That's probably because those bands are what programmers consider "classic rock" in addition to the Stones, Who, Led Zep, etc.
Please tell me, aside from Hendrix, what black artists are missing from "classic rock" programming, because I thought that between Hendrix and Living Colour, there weren't any black artists involved in rock.
That's valid up to a point if you want to narrowly define it. However look at the Rock N Roll hall of fame and the Black representation there. Admittedly there's more R n B,Soul etc there but they are there. It's just unfortunate that oldies radio isn't that inclusive but like you said a lot of that is on the doorstep of big corporate radio.