I am having trouble with the theory of the Airbag being the sole course of the chassis bending.
Assuming the vehicles are loaded when the bent chassis happens, and the vehicle is driven off road some where, with out the Airbags, the Diff Bump Stop would come into contact with the chassis even do so quiet violently. Whereas, with the Airbag fitted, this would be dampened.
Yes, I agree, weight is being transferred to the chassis on a constant basis above the diff with the air bag, but the original design of the chassis surely is such that it can withstand sudden contact from the bump stop.
I'll be interested to know if there are chassis failures like this without the AirBags fitted.
In the early 90's, I was a mechanic for a fleet of vehicles in an underground mine, these things coped a pounding, and some were carrying a lot of extra weight all the time. They were all fitted with better springs / shocks, and nothing else.
Never had damaged chassis, but did have cabin mounts braking away from the chassis due to corregations.