Now imagine if that error said 'Error 11: A memory error occurred. Your program may be faulty or misbehaving. Contact your software vendor." That's miles better than what most things provide.

That one's a good example of why these things are hard. The user could have been running 5 different programs, any one of which caused this error, and MacOS can't point the finger at anyone. Not to mention that the problem could be MacOS itself, or the user being a dunce who misconfigured something. I'm not sure if that error can occur without 3rd party software being involved, but if it can, then that error message might need to be even more vague, helping the user even less. Not to mention it could just be faulty hardware.

A paper manual offering troubleshooting steps for each error would be really helpful. Just 'Error 11. Consult your manual.' and the manual actually telling you what the problem could be is also miles better than what we usually get.