While true, keep in mind there are other ways to enforce these kinds of things. Whenever I read someone quoting Magnuson-Moss, I cringe for two reasons -- the first is that threatening legal action is rarely the best course to take unless it is your last course to take, and the second is that Magnuson-Moss doesn't address everything that could be used to enforce an objective. Tesla may not be able to deny you warranty coverage for the vehicle, but it could potentially deny you other services. For example, Tesla could force you to live without Internet connectivity (mobile app, web browser, Internet radio), if the remote network services are contingent upon certain actions taken by you.
I'm not a lawyer, but I've learned enough about business law to know that there are multiple ways to skin a cat and it's difficult to cover them all. I've also learned enough about business law to know to ask a lawyer.
Of course, over time, these provisions would be tested, new laws would be drafted, etc. In its initial years here, Tesla is aiming for a fully vertically integrated environment and will transition over time as things open up.