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

Competition is the reason for the SQ we are getting today from amps. Also the number of world class speakers available at almost all price points can reveal a great amp from a good amp.

One reason I'm asking:

During a recent visit at my local dealer, I inquired as to why the new amplifier we were listening to was so expensive?

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.

So I'm wondering how much any of these explanations are valid?

I am pleased with all my incarnations of my Bryston amps up top the present 7b3 (I have tried other makes btw). It is much a question of what you like ..
When I put in, now and then, my now ancient Threshold s1000's I still go "Wow - I love these"
What is better?
All depends as usual

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.