[Commander]

A possible reason for lower HP levels in alloy blocks could be structural stiffness.

Instead of the force from the combustion event being transmitted through the rods to the crank cradled in a firm iron structure, it is transmitted down to a crank that is in a not so crystalline structure which will absorb some of the power into itself. The aluminum will have more of a damping effect on the power strokes.

The answer to whether that matters one wit in to anyone here, is most probably : no.