> Apple considers this worth a 30% commission, and 100% of developers on the App store agree, or they wouldn't be on there.
This is where you get it wrong.
If there were other stores for iOS apps and the difference was only Apple's vetting and developers were still choosing to pay Apple 30% vs. much less for some alternative, then you could say that what they're paying for is trust.
But everybody including Apple knows that isn't true in general. As soon as there were other viable stores and developers could put the same app there for a lower price, the large majority of customers would take the lower price over whatever "trust" Apple is ostensibly providing. Unless Apple were to charge substantially lower fees for it.
Which is the only reason they preclude the other stores. If customers actually wanted trust and it could only be provided by Apple then customers wouldn't have to be precluded from using alternative stores because they just wouldn't choose to.
And when that isn't possible, you can't say that people are choosing Apple's store because of trust, when there is no choosing happening because there is no alternative installation method to choose.