I'd go a step further, and say that you have to at least have some transcending of genre. You have jazz, metal, country, and rap artists covering the Beatles and Led Zeppelin. You hear them in elevators and on phone "hold" systems. I think that's a factor here.
I'm a little more conscious of dismissing artists than I perhaps should be, but this is what I was implying when I said Ninja's list is "too expansive". Perhaps I was being too polite.