More significant is the difference in stiffness. Frames are designed around M size. If XS and XL size is made withe the same profile of tubing, the XS will be much stiffer and XL less stiff than M.
This is the complete opposite of requirements, where smaller, lighter, less powerful riders need less stiffness, not more, and bigger, heavier, stronger riders need more stiffness.
Specialized recently designed the Roubaix saying:
"With size-specific engineering and a frame that delivers the best balance of vertical compliance, low weight, and torsional stiffness, riders of all sizes can experience the same ride quality and performance as Boonen."
ie this is a special feature, not a standard method of designing frames.