Is there any concern about any of these music companies becoming, as Fred Wilson would probably call it, "facebook's bitch"?
Depends on which music companies you're talking about. While I love their product and team, RootMusic's BandPages has the biggest liability in that regard. But if a natural behavior for deciding what to listen to on a given day is logging onto FB and clicking on what someone else is listening to (now possible), then being removed from the platform would suck. But FB is too smart to get into the streaming business on their own, and they don't do much else besides drive traffic. So, unless you're dependent on them, which you shouldn't be, then no.