Another advantage to air bags is the weight capacity. Consider a 1 t. truck, rides like a truck when its empty and rides much better when its loaded. With air bags when its empty not much air pressure when its loaded enough air is added to keep the same ride height so the ride stays close to the same regardless of the weight.
The oldest vehicle that I have worked on with air suspension was a '53 GMC transit coach, so they have been around for awhile.
Gus