How do you know their costs don't scale? Maybe there's insurance or compliance requirements that also apply?

And it begs the question - is "cost-plus" the only valid pricing model?

Why would their costs scale with revenue? Cost+ certainly isn't the only valid model. Many people are fine with a 30% cut.

they do - the first 1m$ only cost 15% - It's btw the same with the Google Play Store

The fees scale with revenue - what I'm saying is that Apple's own costs do not scale with the revenue they take from companies on the app store.

e.g. A single transaction of $10,000 does not Apple more than $100 other than the beforementioned financial transaction fee.