Why have capacitors improved so much over the years?

Around 1978 or 79 I had a gentleman answer a for sale ad I had posted for an Audio Research preamp. He made an unusual request of me. He professed to be the owner of a company that was prototyping a preamp of his design. He asked if it would be possible to compare his prototype to my SP6. Who would turn that idea down? He arrived with his unit that was basically just his boards and electronics. A true early stage build. I didn't expect much. I was wrong. We spent a couple of hours using my system and comparing the two preamps to one another. I only remember that he was convinced his sounded more musical and that he was concerned that his choice of capacitors was in need of change. He explained to me what he was listening for concerning the caps. At the time I thought it was "out there" that he would be sitting in his lab and listening to various caps. He must have done something right because his company is still in business and still selling a highly regarded preamp. 

For the interested:
Picking Capacitors - Walter G. Jung and Richard Marsh (reliablecapacitors.com)
No affiliation.

Everything has improved over the years.
Defects introduce colorations.
Some prefer the colorations.

jfd11,
Who was it? Not much of a story without the name.

+1 roxy54!