That is a valid point. I remember reading somewhere that the reason that classic rock bands like The Who and Led Zepplin, who supposedly had "no sell out" policies, are now starting to allow their music to be used in Television commercials is because nowadays it's one of the only ways to get their music out to a wide audience (although I'm sure a little extra $$$ doesn't hurt either)
But like posted up above, often many parties have to agree and all it takes is for one party to say "No" to kill the possibility.