This problem could be mitigated by Apple making older versions of software available. Then you could continue to release updates, and users on older devices could continue to use earlier versions of your app on their devices.

Apple actually partially solves this: as a user, if I have EVER downloaded Older Version X of an app, and then go to download it again, they let me. However, if I have never downloaded the old version and go to download it, they just say “this app is not compatible with your device.” and don't give me the chance to get the older, compatible version. I don’t know why they make this distinction.

Worse are the third party apps where the old version still actually runs, but the developer deliberately blocks you with a full-screen “go away” dialog (I’m looking at you, FlightAware).