the stiffer the chassis the softer the springs can be to compensate
the stiffer the arb, the softer the springs can be to do the damping stuff

i'm sure that a new car will offer much more body ridigity than a 20+ year old sierra will as everything now is done on computers to simulate whats going to happen and everything is now designed to bend one way in an accident to stop the passenger cell taking the brunt of the impact

plus cars are now heavier so this will also play a part in it as well as having bigger wheels to soften the ride quality and yet retain the handling, 40 profile tyres on a sierra give you a ridiqulous ride, but 40 profile tyres on my mondeo mean it still very pleasant to drive even over the biggest of speed hump and pot holes