Earlier quoted context omitted.
Apple provides a service for that 30% though. They handle the payment processing, they build, moderate and curate the App Store apps and they provide a lucrative channel to market for app developers. So allowing Spotify et al to get all the benefits of the channel without paying for it is actually unfair to Apple.
This argument will easily hold if there were any way to have a competing store on iOS devices. Apple banning any competition in that field makes ‘buy they provide value for the money’ look like forcing consumers hand. Not sure if I want to have a second AppStore (APNS, etc, etc.)
Spotify wants to use Apple's distribution channel without paying for it.
That's unfair and doesn't reflect what happens in the real world. If I sell my software through a retail store they still take a cut.