There really is no difference unless we start talking in terms of the very latest tuning mechanics....buttoned pistons etc.
The reason for much better accuracy nowadays is owing to pellet quality which is massively improved. Also choice to pick the best for your gun.
I remember my local gunshop having a choice of about 3....all crap by modern stds. Who can remember the dirt and pellet fragment dust in the typical tin of Bulldogs i ask....and the 3 inch groups they gave in a BSF 55.
My BSF 55 matches pretty much any modern springer with some Crosman Premier for instance and handles much nicer to boot.
Try an Airsporter fed on some Superdomes and compare with some old Bulldogs....then come back.