Nah.
That isn't the vendor of the app making money via an in-app transaction. That's a transaction between two third parties who are not selling something they made using Apple's APIs and distributing a product via the App Store.
You just said
[*]If software is distributed via the App Store and/or leverages the Apple SDKs then they deserve a cut for each. As I see it there are two things apple deserve compensation for - distribution and software library use.
This contradicts that. Banking apps are both distributed via the App Store, AND leverage Apple's SDK.
Also, Banks
are making money via a transaction that occurs within the App, (unless you have a no-fee account and your bank/credit card doesn't have any backend deals with merchants to take a percentage of transactions).
Spotify and the banks
both use Apple's APIs to build the Apps that facilitate the transaction, they both use the Apple's APIs to make money.
Likewise Apps selling physical goods and Reader apps also use Apple's APIs and tools to make money.
The singling out of Digital goods continues to be justifiable only as an arbitrary business decision, which, given that I (and the EU) believe Apple should be acting as a neutral gatekeeper they shouldn't be doing.
- I'd suggest that the quality of the Apple (not just iOS) software libraries is worth some amount. However if apple want to take some amount of money for that they need to provide the option for development not using said SDKs.
If developers want to host their stuff elsewhere via another store, they should still pay the royalties for use of the SDKs.
These are two things that Apple needs to be careful of. I think that if the EU is serious about open access and Apple continues to try and monetize its SDK access then we could see the rise of Electron style Apps on iPhones. Avoiding the use of Apple's IP as much as possible.
In recent years Apple moved from "the App Store commission pays for running the store" to "the App Store commission pays for IP and SDK access" and this move has mostly been internalized and while I agree that Apple should be allowed to charge a fee for API access in principle I think that doing so will ultimately undermine the platform.
There is a reason that open platforms (without a gatekeeper) typically do not charge for SDK access, it is because they
want developers to use their SDK because it makes the platform better. Apple's control of iOS (gatekeeping) has distorted this normal trend because they have been able to force devs to use their SDKs.