The only way Spotify can avoid this problem is by becoming too big to ignore, a la iTunes for digital distribution or Walmart for physical goods. At that point the labels have a hard time saying "we're going to pull our inventory unless we get a better pay rate" because though it may dent Spotify's customer experience, it will also mean a substantial hit to the bottom line of any given label who walks.

If you can't get to the point where you're the 800 pound gorilla, however, you are very much still at the mercy of the content owner.