They bought exclusivity to as many top podcasts as they could in order to start centralizing podcasting on their platform. Eventually enough momentum shifts, and all the other podcasters have to go where users go, spotify. They may or may not succeed. Either way, it's not just "buying premium content." It's an attempt to seed a monopoly. I doubt that what they spent is even theoretically justifiable as a self contained business proposition.
The whole thing is quite sad. Podcasts are/were one the the free digital medias. No mediation. Standard protocol. The client is just a client. No one tells you what to say, or controls who listens to what. I wish FB and youtube were that.
We the geeks have done a terrible job of defining and promoting digital freedom. Failed to find a way that doesn't sound like a paranoid eff rant. I don't think Joe really understood that RSS is a Free (as in freedom) media, perhaps the last. He probably thought about it as Youtube-vs-Spotify, with Apple and other RSS clients being more of the same.