iTunes had a formal sale price, and it still led a catastrophic collapse in music sales revenue (https://money.cnn.com/2013/04/25/technology/itunes-music-dec...) which only ended when Spotify became big. The point of a comparison is to understand whether Spotify is doing something that could be fixed to get more revenue to artists, or whether the economics of selling songs for money just don’t work very well in a digital world.