After a purchase the app developer is the one providing content, customer service, app updates and bug fixes, etc. It stands to reason that a customer is doing business with the App developer not Apple. In all of your examples, they are products where the company setting the rules of the transaction is the same one that is standing by the product itself.
It seems completely reasonable to me that the provider of a good or service should be able to communicate freely and directly with their customer about something as core to the transaction as their options for paying for the service.
When you buy those products previously mentioned, what options do you have to pay? You don't pay Nike for the shoes when you buy them from the store. You don't pay the author or the publisher for the book. Those people have already been paid by the vendor at the wholesale rate. You are reimbursing the store plus their markup.
The store also doesn't generally review the boxes of shoes and ensure there's no references to nike.com on them, and if they did, there's plenty of other stores for Nike to sell at.
If you want the analogy to make sense, let's assume there's exactly two places that sell shoes and they have a stranglehold on the market, and they both mark shoes up the same amount and far more than they would if there was competition between them on price, and they refused to allow any reference to nike.com and how you can get shoes far cheaper there on or in any of the packaging.
That would be a very dysfunctional market, and I think the reason would clearly be the anticompetitive practices that prevented competitors and that resulted from them not competing on price.
It is even worse than this, btw, as the markets are disjoint: there are two places to buy shoes, but virtually all customers shop at either one store or the other store (for practical reasons of cost and convenience that are similar to those seen with someone having to buy things from a store in a different physical region of the country than where they chose to live), making each store separately a monopoly over its relevant market.
The retail analogy doesn't quite fit. Apple isn't just the shoe retailer[0] they're also the company which supplied Nike with all of the sewing machines and stitching yarn that was used to assemble shoes made with Nike leather and rubber. Nike signed an agreement with Apple which says that in return for an endless supply of sewing machines and yarn, Nike must split the final revenue with Apple.
[0] And even retailer isn't quite right. What the App Store does is less akin to the wholesale-retail model and more like the agency sales model.
I think the more reasonable analogy is that Apple is a Mall and the different apps are stores in that mall, but in this mall they don't charge you a flat monthly fee, they charge you a percentage of your revenue and to make sure you aren't cheating on that they make you use their cash registers and credit card machines.
As a consequence there are incentives for the stores to decrease the amount of money they make in the normal way and they instead try to find strange ways to make money that the mall doesn't get a cut of.
For example if you buy shoes at the shoe store they will send you new colorful shoelaces every month if you mail them money.
But every now and then a store will come up with clever new way to make money that doesn't give the mall its cut and then the mall throws the store out and leases its space to a competitor. Or just announces method X of making money also needs to give us our share.
In my personal opinion (and I recognise that this is a controversial view on Hacker News) Apple should be entitled to the same thing Epic Games asks for—which is the right to decide how much their intellectual property is worth when used by other developers to build commercial products.
I think the issue is that once you become a monopoly (as Apple's store is: users choose--for any number of reasons where this is frankly likely only one small one where they might be as pissed off as anyone else--between two stores that also-frankly have similar terms anyway, meaning they don't really have a choice anyway, but then developers can't choose: they are held hostage to access that market), you lose some of the "rights" you have as there is no way to compete on terms. If Apple were to separately say "you can either build on UIKit and Metal, in which case we take 30% of your revenue... or you could use HTML and OpenGL, in which case, well, good luck?" then I think a lot of developers would avoid Apple's frameworks... and if they could explain why to the user--that every time you buy a movie from us you are spending an additional $1 for the UI framework Apple is providing--they would agree wholeheartedly, as that shit adds up fast.
It seems completely reasonable to me that the provider of a good or service should be able to communicate freely and directly with their customer about something as core to the transaction as their options for paying for the service.