Their product is far from unique, and only really interesting because it has better PR, more apps, a better library, and a slightly more legit licensing setup than the competition.
Slightly more legit? I think the phrase you are looking for is "completely legit, as opposed to some of the others who are lawsuit-bait-on-a-stick."
After all, it would be a lot easier for Facebook to replace Spotify with another provider than it would be for Spotify to replace Facebook.
Only if that other provider had the same kind of licenses with the record labels. At this point, Spotify is far ahead of the pack at that game.