I regularly shop at three different grocery chain stores. It's way easier for customers to switch between them compared to being locked into the Apple app store.
You’re right about the ease of switching. I think buying a wholesale club membership card is more analogous. You could buy a Costco card and a sam’s club card if you wanted, but there’s likely not many people who do. People actually prefer the shopping process at Costco for example, and they pay a yearly fee for it, just as people like the shopping/app purchasing experience on an iPhone, and they paid a substantial amount of money for the phone.
100% of iPhone users use iOS doesn't matter what the total smartphone use percentage is. It was the same when railway Barron's started capturing the other markets when they owned the railways each railway barron owned their own track and people had alternate routes
The sale of apps basically died years ago. Most of the revenue from apps is either coming from in app purchases of consumables or subscription service that are cross platform.
Music that you bought from iTunes has been DRM free for ages.
Most movies purchased from iTunes are transferable to Google Play, Amazon Video and Vudu vis the Movies Anywhere app.