> The existence of a third-party marketplace doesn't change anything about that situation other than forcing the OEMs to compete more
It changes one other thing, customer experience. Apple believes fewer problems with a device is a better customer experience and with a better experience customers will return time and time again to purchase their products. It's not right for everyone, but I believe that is true for some people.
In order to deliver such an experience, they have to backup their products with exceptional service, and they do a better job at this than most companies. Now, that level of service is not cheap, not to mention most people don't want to deal with support anymore than they have to. So, to make that level of service feasible, they need to reduce the amount of service you need. For that, their solution is to lock the operating system and hardware down very tightly and vet every piece of software that can be loaded on to the phone.
For some people, all of that sounds terrible, and those people will choose not to buy Apple products. For others, it sounds like a carefree experience and they will choose to accept the trade offs for the benefits.
Bringing this full circle to your car example, there is a lot of crossover between these two worlds. Most cars have very good warranties and pretty amazing coverage while you car is under warranty... sounds a lot like Apple. Like your car, there are certain limitations on changes to hardware and software if you don't want to void that warranty. In other words, you are limited as long as you're under warranty.
So, I can appreciate Apple's desire to lock things down... yes, it benefits their bottom line, but I think they also do it for benefits to the consumer. Now, like your car, when the warranty runs out, the OEM service isn't quite so special anymore. The OEM doesn't care what you do at that point because you're on the hook for everything. I think the same should be true for iOS devices -- when the warranty runs out you should be able to request an unlock and then you can sideload whatever you want. If you like Apple's protective measures, you can continue to run in safe mode. Apple would never voluntarily do this of course, because that would increase the value of old phones and potentially deter the purchase of new models. But, it might be a strategy that the feds could pursue.