This is probably correct for symphony orchestras and baroque chamber music, but it's not true for modern pop music or some fusion jazz. (In my measurements it's also less true for Beethoven than Mozart, for example, but I digress.) I doubt you listen to Kanye West or Cardi B, but the bass line below 80Hz is powerful and nearly continuous. Fusion jazz often has strong synthesizer bass lines. I'm not a fan of the popular music either, but you and I are in the minority.
The point is not to confuse sensitivity with efficiency, which Swerd explained well, but that's not what Jerry asked initially. I figured he was knowledgeable enough to already know the difference between sensitivity and efficiency. As for the comment about the inefficiency of small sealed subs, true, but how is that relevant to his question?
Again, this is true for symphonies and chamber music, but many action movies (which I generally don't watch either) and pop music genres do have strong bass lines, and with a crossover at 80Hz, like most AVRs use, I'm certain powered subs of whatever cabinet strategy are indeed off-loading the primary amplifiers to some significant degree, and it's not "absolute nonsense". I had a few people who want to hear what their music sounds like on my primary system, and out of curiosity I've fired up my RTA software, so I'm not guessing about what's on a Kanye West album.