Good test for volume level's, I don't think anyone would disagree that more power louder sound. But as Alan wrote
"Specifications (distortion, noise, etc.) of preamp-processors and power amps are usually a bit superior to an A/V receiver, since there is better internal physical separation of wiring pathways (more room), hence less chance of interference (and resulting noise) from nearby hum-causing component parts."
Can that be measured?

A computer once beat me at chess, but it was no match for me at kick boxing.