Interesting and I was wrong. While that might make for a good case why Apple should be compelled to allow the side loading of apps (especially since an App can be sandboxed and couldn’t possibly damage the device, a key criteria in the link). It still makes it hard to win an antitrust case against Apple. If you defined the market for Ford radios as to only include Ford-manufactured vehicles, then every single car company is a monopolist. Defense would push back that Ford competes against GM and Tesla, not against Bose and Sonos (in my prior analogy), so as long as consumers have choice of cars, then Ford shouldn’t be subject to antitrust actions and remedies in regards to radios.