Re: What's wrong with Apple's patching?
All the devices not being supported with iOS 13 have 1 GB of RAM. Not sure why a cutoff based on RAM is any harder to justify than a cutoff based on 32 vs 64 bit.
Apple has issued patches for "unsupported" versions of iOS previously, not only the recent "GPS overflow" patch for iOS 10 & 11, but produced a patch for the "goto fail" bug for iOS 6 after its support had officially expired. If there was ever an iOS bug being actively exploited in the wild, I'm sure Apple would issue a patch for older versions of iOS to close it. But they aren't going to issue patches for every bug that's found forever.
If I recall, I believe Microsoft adopted a similar stance with Windows XP, there were a couple bugs that had exploits circulated where they released patches after its "end of support" date had passed for all XP installs, not just those getting the high priced extended support. Hopefully they will do the same for Windows 7.