Amplification: what are the biggest advances of the last 40 years?

Getting the neurotically obsessed to believe that five-figure amps are somehow sonically superior to well-designed four-figure amps!

bobbydd (OP) later said:

I inquired as to why the new amplifier we were listening to was so expensive?

Ok, so that's a different question than the original (after all, computer technology has improved massively but home computers aren't more expensive). I'd put the price change down to economics:

First, a larger number of people can afford to spend more. This comes from rising middle classes in traditionally emerging economies  (so there are just many more people who can spend money on luxuries). It also comes from increased concentration of wealth -- rather than having 100 people who can buy 100 nice-but-basic systems, there's one person who can spend lots on a single expensive system.

Second, the production of stereo gear is generally slow (low supply) so it's in the company's best interest to set high prices.

I'd also guess that better information (the internet) leads more people to chase fewer brands that are considered to be the best, further concentrating demand for (and therefore pricing power in) a few ultra-premium brands.

This has been going on for a while in French wines, and I suspect many other luxury products.  I'd say these economic forces contribute much more to rising audio gear prices than any of the component or design changes.

@bobbydd  

I inquired as to why the new amplifier we were listening to was so expensive?

The parts and labor that go into a quality point-to-point constructed amp are incomparably expensive vs 60 years ago.  Mass produced, PCB-based HT receivers can be churned out much less expensively (relative to inflation) than products even in the 70s.

@bobbydd

The reply was something to the effect that "well, the technology and parts quality of these newer generation " units are far beyond what was possible a few decades ago. Also, that circuit design has advanced tremendously as a function of technology.

This is a valid statement. Although it’s not a stark change like the discovery of semiconductor chips, high-end audio is uses both technology and art. In our small niche high-end audio market, intense competition leads to increasing better sonic designs over time. Take prolific amplifier designer Nelson Pass for instance- his decades of designing experience has influenced his current offerings. Also, the quality of audio transformers have made significant sonic improvements.

Even internal parts can be very expensive such a Takman, Vishay, Mundoff, to name a few. Custom transformers can also be pricey. 
Also with better audio component designs (like speakers), we are better able to hear differences in the quality of amplifiers. 

That’s why we pay (and sometimes pay n pay n pay…) for these sonic improvements.

And please, none of the banal "it all matters" comments

The entire audio chain matters, but one’s system must be resolving and transparent enough to hear the differences such as to the “fool you it’s real” level. While one can throw in a quality amp and gain sonic improvement, if the rest of the system is not to the same quality level as the new amp then the rest of the system is holding back what the amp is capable of performing.

The biggest advantage to better components in the last forty years was the advent of the compact disc and the dvd and blue ray which caused the amplifier to put out more power and dynamics to meet the demands for the new mediums. The other key components have all taken a step back in technology and sound since the start of the ipod era because of the advent of computer style electronics instead of audio grade eletronics. As for speakers they have all taken a backwards turn since 1965.