They will backport fixes for SOME issues for SOME phones. The further back you go, the more likely you will be ignored. I do have some sympathy for Apple on the difficulty of supporting old phones etc, but let's be realistic, too:

1. They leave you with a strong impression that all phones and all iOS versions are kept safe by dribbling out a few fixes from time to time for older devices. That's probably worse than on Android, because you think it's safe, but it's not.

2. The whole point of getting your hardware and software from the same place was precisely because then you knew they had a limited number of things they had to support, so it'd work better. If they have too many things to support, then maybe that argument starts to fall apart.