Aren't most torque ratings on bikes for the bolts themselves, and not for the component that that bolt is actually being used to clamp? The indicator eg. written on a stem, doesn't know the material or brand of whatever handlebar you may choose to stick in its clamp.

Then there's a variable in the number of bolts that a clamp may use, and then an additional variable in the shape and surface area of the clamp that's being used to clamp to a component. eg. 2 vs 4-bolt handlebar clamps on stems; varying designs on seatpost saddle-rail clamps.