Adele and Spotify - not quite yet

Fast Company had an interesting article (read here) about how Spotify turned down Adele's album 21 (which just one a Grammy for Album of the Year).   Essentially, Adele wanted her album available to paying subscribers of Spotify, but not to the subscribers using the ad-based version of the service.  Spotify wasn't willing to change the structure of their service (currently both types of members get access to the same library) to accommodate this request.  I wonder if this is a slippery slope for Spotify, since in many ways the popular albums available for free subsidize a substantial part of the their music library, and as soon as other major artists realize this the Spotify service might lose some of its appeal.