Agreed. I simply wanted to point out that the car manufacturer does not actively try to prevent the car owner or the installation shop from installing a stereo

Agreed. I simply wanted to point out that the car manufacturer does not actively try to prevent the car owner or the installation shop from installing a stereo. However Apple does this with their devices. Everything must pass through Apple even after the sale is complete and the user owns the device, and that is just absurd. I can't imagine what older Macs that we used for audio applications would have been like if all software had to be approved by Apple. Apple does not have the expertise to write all that software. When I say Apple's strategy will backfire I mean that the more tightly they try to exercise control, the easier jailbreaking is going to get. The auto manufacturers may have made it very difficult to do stereo installations on newer models but they are not actively trying to interfere with stereo makers and installers after the car is sold. And why should they? The buyer made his choice when he bought the car whether he wanted any factory installed audio options or not. If after the sale the buyer wants to buy parts, or get service from an authorized dealer, she can do so. But the manufacturer does not try to interfere with her choice to get service (e.g. stereo installation) elsewhere. Imagine if every car stereo maker had to get approval from car manufacturers and could only sell their products in the manufacturer's distribution centers.