There are differences in blade tech, just as in GI and SGI tech.
Some of the earlier blades were just that... same thickness heel to toe, sole to topline. Fairly even weight distribution throughout.
Then came rearrangement of metal, and thus weight, to incorporate a wider beveled sole (bounce), and more mass behind the center of the blade (muscleback).
Various iterations of the general theory ensued, leading eventually to the cavity back of GI clubs and the very wide soled, rear center of gravity (through the use of a slot or void behind the face) of the SGI.
I play an older set of Wilson blades with a fair amount of bounce and a muscleback that is heavier towards the sole. Wilson has come somewhat back toward this type of blade in their FG62. If I should ever give up my classic irons, I will go with the FG62 and probably feel right at home.