I get that it's positioned itself as a platform, but that doesn't mean it's shorn of a duty of care to its customers. That specifically, in this case, means providing me with the means to access this app. If that means the option to roll back the ios, meaning my carplay features no longer work, that should be on me, but it should be up to me.
If I had physically bought the item, I would still own that item and have the choice to use it in an older system, or simply use it as an expensive paperweight. In this case, they have removed all trace of me ever having owned or paid for this app, and other than possibly jailbreaking my phone, or finding out nifty ways to roll back the ios (clearly not that simple if no-one here has been able to point me in any direction), I am left out of pocket with no recourse and nothing to show for my money.
I would argue that the whole methodology is crooked, that any app designed for ios X necessarily needs to be compatible with ios > X, whether that be on the heads of the devs to conform to future compatibility issues as proscribed by the platform, the platform to ensure that no features get written out, nor do any new features render previous features impotent, or on both their heads. Not like the app market isn't overly flush with money.
Anyway. It really doesn't matter much, just another way us fools who don't care to read the TOS get parted from our money by people who aren't quite rich enough yet.