I'd agree up to a point with some of this. However, I'd have to take issue with "Everything about amplification and electronic theory was known and done as of about thirty years ago." I did electronic engineering just less than 30 years ago and 100% of what I was taught about high-power semiconductors has been obsoleted, and most of the stuff that obsoleted it is now obsolete. So, while the analogue theory may not have changed all that much, what can be achieved has been revolutionised about twice. If you look at commercial systems that get used in venues, studios, etc. then it has been furter revolutionized by DSP, active speaker technologies, computer control, adaption to environmental factors, etc. And when I was studying electronics, the 70s seemed like the stone age because they had almost no FETs and SCR stood for saturable-core reactor. When I studied amplifier theory, Class A and Class B amplifiers were reality and Class D was a new development just coming in and certainly not suitable for audio.
These days I think you'd be amazed at the quality that comes out of 6" drivers. I sure am. I used to own "your father's system" and it had 12" woofers, only because I couldn't afford 15". These days I have a pair of speakers that has 6" drivers and they are pretty flat down to abut 35Hz - about what you got out of 15" drivers in the 70s. They sound great (much better than my father's speakers) and don't need a sub for any music. (But the sub is great for movies.)
I tend to agree with the article that what people care about has changed. Sound systems are used to watch movies and listen to ipods. So naturally you want 6, maybe 10 channels rather than 2. That is a lot more amplifier. And the source material has degraded, at least for the average person who is prepared to shell out a 1980 $500 for a receiver. How many people on this list actually sit down on a regular basis and listen to an album right through? I know I do it rarely (although I am trying to change that) these days, but 15 years ago I did it regularly.