I can't explain it, but I expect some of the techies here may shed light. I can tell you that ** in my experience **, rated power output has little to do with quality of bass produced by amps.
Some amps I've owned seem to boost bass response (Parasound, Phase Linear, and others), while others have subdued bass (B&K, Conrad Johnson, Ayre). note - keep in mind my experience is with limited models of the brands I'm citing. The two brands I felt produced the tightest, most balanced bass were Bedini (100.100), and Electron Kinetics Eagle 2. The Eagle 2 has iron fisted bass control and response - the nicest of amps I've heard. Another note - this is based on my experience in my home, my system.
Some amps I've owned seem to boost bass response (Parasound, Phase Linear, and others), while others have subdued bass (B&K, Conrad Johnson, Ayre). note - keep in mind my experience is with limited models of the brands I'm citing. The two brands I felt produced the tightest, most balanced bass were Bedini (100.100), and Electron Kinetics Eagle 2. The Eagle 2 has iron fisted bass control and response - the nicest of amps I've heard. Another note - this is based on my experience in my home, my system.