Go look at a car from the 90s with a DIN or double-DIN stereo, then go look at one from the past five years, where the prevalence of nonstandard sized stereos has gone way up, as has the complexity of how tightly coupled they are to the rest of the car. Those are the hoops. I don't think the manufacturers are upset at all that one of the side effects of this trend has been to make aftermarket head unit installs a lot less convenient.
And I don't know any manufacturer that will sell you someone else's head unit as an aftermarket piece. It's up to you to find out how to take everything apart and fit something else in there on your own, or to find someone who knows—basically, jailbreaking your dashboard. Except you generally lose stuff (like steering wheel controls), while I hear jailbreaking is pretty painless these days.
Edit: Apple's app store isn't some third party stereo store, it's a store owned by the manufacturer itself. And car manufacturers are famous for having highly priced proprietary replacement parts, especially when it comes to electronics like stereos, if you aren't willing to deal with an outside store/brand. I really don't see any way Apple's less flexible with the iPhone than a car manufacturer is with their cars.
And I don't know any manufacturer that will sell you someone else's head unit as an aftermarket piece. It's up to you to find out how to take everything apart and fit something else in there on your own, or to find someone who knows—basically, jailbreaking your dashboard. Except you generally lose stuff (like steering wheel controls), while I hear jailbreaking is pretty painless these days.
Edit: Apple's app store isn't some third party stereo store, it's a store owned by the manufacturer itself. And car manufacturers are famous for having highly priced proprietary replacement parts, especially when it comes to electronics like stereos, if you aren't willing to deal with an outside store/brand. I really don't see any way Apple's less flexible with the iPhone than a car manufacturer is with their cars.