It's not a common A-body problem but a common car door problem.
The striker post isn't supposed to carry the door. If the door hinges are serviced regularly there isn't a problem.
I'm gonna disagree with you on this one. Since I've owned my '69 Valiant, I have seen or heard of this little nuisance a lot. I work at a Chevy restoratoin shop and can't say I have ever seen this happen on any of the GMs that use this type of post. (Not saying it doesn't, just saying out of the ones I've seen in the past fifteen years, I ain't seen it).
You are correct, nothing beats proper maintainence. The latching mechanism is a part of the vehicles integrity, though. Proof would be opening the doors when the vehicle is on a lift. Or, referencing my 73 shop manual for my Roadrunner, it actually states that the striker is supposed to pull the door down when latching.