I don't know. You aren't laying out any logical reasoning behind what you're saying other than "you feel" that way.
Once my car's warranty expires should Chevy be allowed to enforce a mandatory recall in which they change the car to prevent after market products from working in it?
Depends if your Chevy gets the newest (regular) updates from the manufactory. There's nothing to stop you to use the old version of iTunes that as far as I understand still works.
The logical reasoning is that - if they don't have to support it, they can actively block it. If it is a standard, they should actively support it. If it is not a standard, they can actively block it.
The reasoning is like running a firewall - you block everything, then open up only the services you need open, and only from the sources you need things accessible to.
By analogy, Apple can make it so that nothing syncs with iTunes, then open it up so that the iPod and iPhone do.
By doing that, they cut off anyone ranting that iTunes is rubbish because it crashed when syncing their music (unmentioned: to a third party device).
Microsoft picked up an incredibly bad rap for bluescreens, enormous numbers of them were caused by poor device drivers and shoddy third party software. Apple has little benefit in allowing El-Cheapo Music System to sync with iTunes, but lots of potential downside (support calls, lowered image of Apple, people migrating away from the Apple ecosystem towards less profitable accessories, buggy integration that requires development and testing of software update workarounds).
Once my car's warranty expires should Chevy be allowed to enforce a mandatory recall in which they change the car to prevent after market products from working in it?