But Apple's argument is that the AppStore is what is providing the value. Why the arbitrary decision to mandate in-app payments for digital goods and not on services or physical goods? Uber is getting all the benefits for free that Apple says Spotify wants. What rational justification is there for carving out digital goods as an exception? Apple isn't providing anything other than app distribution to Uber or Spotify, why treat them different?
That's going to be the problem for Apple when the EU Commission is looking at the complaint. They are putting in place restrictive rules that only affect markets in which Apple is a direct competitor. Make the rules uniform for all developers and things would at least look better, but the customer experience would go down pretty quick.
Could you imagine if the choice in using the Uber service was to pay either $10 for the ride plus an additional $3 to Apple by using the payment method in the app, or having to log into a separate website and pay Uber directly every time to save that $3 fee? The confusion would be rampant and the anger widespread as people suddenly saw their $10 ride cost $13 just for using the app. That is exactly what Apple expects anyone making a digital purchase from Amazon, Spotify, Netflix, etc. to do.
On the other hand, allowing Spotify and other retailers of digital goods to use their own in-house payment system through their app (just like Uber does) would be a fair option that would cause the least amount of disruption.
Spotify isn't asking for special treatment, just the same treatment as other providers who sell goods and services through apps distributed through the AppStore.