Fantastic to see a classic reviewed, and rather satisfying to see that measurement indicates that the reverence some of us have for classic hifi is not just rose tinted nostalgia.
In terms of what happened, in some ways we as consumers got what we wanted. The big Japanese outfits had a sort of engineering arms race in the 70's and 80's to develop the ultimate measured performance and invested serious money into their engineering and R&D. The resulting products were manufactured to a staggeringly high standard. Now you might think consumers would welcome this, but no, a culture of golden eared disdain for measured performance evolved, aided and abetted by reviewers who waxed lyrical about shoddily engineered and made boutique gear which had terrible measured performance. Products like this were derided as being "sterile", soulless, bland, lacking all the usual audiophile subjective terms blah blah blah, is it really any wonder that some Japanese companies realised which side of their bread was buttered and embraced that culture?
I actually think the mass market move away from stereo systems and towards viewing audio equipment as a commodity in the late 90's and on was actually much more rational and sensible than all the audiophile nonsense that sustains the high end bubble. I find it all very sad as a good set up (and I mean good, not expensive, it need not cost a great deal) does make listening to music more enjoyable.