How in the world is an App Store infrastructure? It’s a proprietary platform. We have the Web as the free open platform, anyone can use any device to visit any web site. The App Store is a premium alternative.
If Comcast (Google) and Verizon (Apple) both charged 30% markup on anything you bought on Amazon, would you think that's reasonable? Without them, you wouldn't be able to purchase anything at all, of course!
Electric, water utilities are private companies.
There will likely be a legal framework that develops to define a threshold and definition for when something constitutes a "platform" with sufficient market size such that competition within the platform be allowed.
The App Store is a more premium alternative to the Web. It’ll never be a monopoly — every iPhone comes loaded with Safari for alternative ways to engage with customers.
Pretty evident when you go through the thought experiment that ecosystems/platforms, with high costs of switching, are a new form of monopoly (at sufficient scale)