Earlier quoted context omitted.
The own the platform, they designed it, built it, and maintain it. They have every right to set the rules for it.
Until regulations steps in, and mandates to be more fair and open, or to break up the company, or to allow multiple app stores (by competitors). At the end of the day, and iPad is a general computing device, and it will probably be treated as such in courts, where there are precedents on this.
b) There are no precedents that state that a platform must have competing App Stores or make them freely available for anyone to publish. In fact the opposite is the default in companies today e.g. PSN, XBox, Tesla, Shopify, Salesforce.
If you have case law that contradicts this please by all means provide it.