This may make good sense from spotify's point of view without knowing all the facts but it looks like it makes very little sense.

Spotify and facebook are two unrelated services that users get to apply the 'binary or' truth table on. None, one or both. To force users to use both communicates that spotify sees only one possible exit strategy at this point, facebook or bust, and facebook has just strengthened their hand in the negotiations for any buyout to the point where spotify is now basically just an extension of facebook.

If spotify does not want to play ball on fb's terms from now on facebook has the ability to pull the rug right out from under them.

I wonder what the missing bits are here, there has to be a lot more than meets the eye for spotify to do this.