Over the years, AV receiver manufacturers found ways to rate power less conservatively to give the illusion of more.
We all know this, we see it all the time.
But how did this trend start?
Gene-
What I recall happened when I became Yamaha's Product Manager in 1983 (from Kenwood Car Stereo) was as follows:
The Japanese audio manufacturers had all just decided to standardize component widths to 430-435 mm while mini component width which was common in products in Japan and I think the European market at the time was standardized at 350 mm. With this move the gargantuan high power receivers like the popular Sansui 5000 which dominated military exchanges all of the world ceased to be produced. So all manufactures were now tasked with getting (true RMS) higher power out of this much narrower, standard receiver width.
Second, Yamaha was really concerned with meeting UL specs because they and all their competitors were trying to come out with and market what they wanted the American audio consumer market to believe were proprietary amplifier typologies that "sounded better" than their competitors. For instance, Yamaha came out with a pyramid shaped amplifier with "X-power". But unfortunately X-power was based on Bob Carver's small 200 Watt per channel 6" x 6" x 6" cube topology. So I recall the bottom line with X-power was Yamaha's US-based certification engineer (named Lucky, no joke) told me at one time he had blown up 25 pre-production prototype amps Yamaha, Hamamatsu, Japan had sent him, none would pass UL.
Next, Yamaha Japan started asking me about the old IHF, Institute of High Fidelity power specs that Julian Hirsch (deceased) of Stereo Review followed which is essentially the same 20Hz - 20kHz, 8 ohm @ 0.XX% spec (at that time in the late 60's and early seventies still called cycles per second) that you are trying to get back to now. Yamaha's engineers told me they were having a really hard time meeting the full 20 Hz to 20 kHz bandwidth power spec at 8 ohms, how about if they used 6 ohms, would that be okay for our U.S.-only receivers? In the same breath they promised they would keep the 8 ohm 20 Hz to 20 kHz full bandwidth spec for Yamaha's integrateds and separates which were sold world wide.
It has been decades since Yamaha receivers first wowed specialist audio dealers (six hundred selling Yamaha at the time) and baby boomer audiophiles like me when introduced in the early seventies. At that time (wide and deep) Yamaha receivers stood alone against lesser manufacturers products which claimed 500 watts!, 1000 watts!. The power amplifier ratings game cycle as you have so astutely observed has sadly come all the way back to where we were then.
The one good piece of news I can share Gene is that when I began designing speakers for Marantz in Sun Valley, CA in 1971 Dawson Hadley (deceased) Marantz's chief engineer of American-built integrated's and separates started me off wiring the internals of my prototype speaker designs with twisted 14-gauge wire, a trick he had learned from JBL's Bart Locanthi (deceased). Physics don't change, but sadly a new generation of snake oil sales and marketing slubs seem to be ever-present. Sigh...