They probably could live with it but I can understand why it feels like an artificial cost that Apple came up with. It would be an understandable cost if they were selling the Spotify App through the App Store and using the actual store infrastructure for supporting Spotify... but they are not.
The app is nothing more than a portal to the entire Spotify infrastructure, it doesn't weight anything to Apple.
And then we have the subject of the direct competition, Apple Music doesn't need to have their profits cut in 30% because they are owned by Apple itself.
And it's even worse if they are using Siri, Homepad and Apple Watch to make Apple Music more appealing in comparison to Spotify.