That was about a patent infringement case though, wasn't it?
The word choice of "threatening" (rather than merely "saying" or "announcing") is quite telling.
Are they in a position where there withdrawal from a market would be a "threat" - and why?
OK.
Since you said, "in order to distribute your game, the store can take whatever you want" and "Storefronts have markup for any product you sell on them" I will be rephrasing my earlier statement:
? You statements really lead me to believe the core of what you think is "Since Apple created iOS, they can treat every in-app running on their phones and OS as if it were distributed/sold by them".
My take: In-app purchases such as music and video streaming subscriptions or even in-app coins, character armour/enhancements etc. are not created, sold, distributed or delivered by Apple. Neither does the act of "flipping a switch" sell, distribute or deliver anything from Apple to the end user. If anything, that's merely a legal fiction created by Apple's developer terms and conditions.
Apple shouldn't (be allowed) to arbitrarily charge for things they did not and do not deliver.