I agree - they're definitely putting the customer's security first. If people want to use an open environment, the web browser is always available on iOS anyway. Apple are completely within their rights to restrict their application platform.
it is like to say that GM is completely withing their rights to restrict where you can drive your GM car. Mind you, that is coming in pretty near future too - giving all the computerization/connectivity/self-driving of the cars which would make the cars into GM's "application platform" with DMCA protecting such a platform too like it protects Apple/Google/FB/etc...
i wonder whether you're intentionally skipped that part or just don't know that in case of non-jailbroken iPhone the "GM dealers" is the only way to get "aftermarket accessories". There is no "if they want to sell their products through", instead there is "if they want to sell their products at all".