My son has an '81 PK Ripper (looptail) that is still intact after decades of bashing.

I ride an '89 Raleigh Technium PRE that is still in perfect condition. Just want to add that harshness of ride does not depend on the bike's engineering or lack of. It depends on the rider's butt and arms.

Stress failures? Sounds like some get more stressed over the aluminum than what the aluminum itself does.