So how is "owning" a CD any different from Spotify?
Also, the value of a song diminishes the more you listen to it. Seriously, even if you love a song, put it on repeat for a day and you probably won't listen to it again for a couple of months.
So it's not like Spotify customers will one day buy the music, unless they really have very specific needs, like being somewhere with a bad or expensive Internet connection, but if you subscribed to Spotify in the first place then I doubt that.
Because if you quit Spotify you lose all the music. The CD you can keep for life without having to pay $10 every month.
Even besides the licensing/ownership fact (you have always purchased a license to listen to the music privately), I bet there's more music released in a given day than hours in that day. I keep thinking that the model where you can just listen to whatever you want for a flat flee makes a lot more sense in this universe.