It doesn't take too much time listening to Pandora before you realize how narrow their library is in reality. At this point, if I put on a station I can genuinely predict what song is going to come up, at least I can guarantee it won't be anything new.
As for Spotify, its truly no more than mediocre. Just like Pandora. So, if some mediocre music listeners want to listen to mediocre amounts of mediocre music, they can go crazy for all I care. But any true music listener knows that nothing beats your own library.
As far as I'm concerned, the audience that misses out on those artists, and the artists themselves that don't earn what they should from streaming, wouldn't have been in touch anyway. If I really want to learn about jazz, classical, or Radiohead, I think anyone with common sense can come up with a better place to look than Pandora.