Yeh i think you are right and wrong Tails - lol
Front and rear suspension is the same type (mcpherson strut and IRS) but the suspension setup, refinement and tuning progresses immensely from model to model.
I have a VP Calais with IRS and compared with the VX Execs IRS I have driven, its like comparing a BMWs suspension with a Hyandai Excels.. okay so NOT that much different but definately noticable.
Remember shockers and springs are better not to mention newer, more expensive units, and also tire size/profile as well as body shape and aerodynamics make a big difference.
Also other little things like seats, sound deadening and cabinet/body build quality will make a lot of difference also to the feel.
Drivers also expect that every new model handles and drives better, goes faster, uses less fuel, looks better and gets them more chicks than the model it replaces!
Thats my 0.02cents........
PS, back on topic - VS is a very nice car - go and see if you can find yourself a Berlina thow, they have a lot of factory options which keeps driving a bit more enjoyable.