The arm angle that the pedals are attached to is the culprit from what I've seen.
The Auto trans and the Standard, have the same angle for the brake pedal arm. The auto, brake pedal is just slightly larger in surface area.

From your pick above, this provides an understanding as to why. It is cheaper to use the same arm on the Auto as it is on the Standard. Seems that the Factory just adds two identical arms for the standard and uses the single for the Auto.

The angles appear to be designed to allow the Clutch and Brake to exist in that space. It would be more expensive to design a seperate arm for use in the auto trans model.

My .02 is that it couldn't be that expensive.
FWIW.