Analog gear has improved, but that's not the same as "advanced."
Everything that has happened in analog has been evolutionary rather than revolutionary, and mostly in the areas of reliability and performance delivered vs cost (which is why plugging the cost of a vintage piece of gear into an inflation calculator doesn't tell you squat about what it would cost to get the same level of quality today).
The most obvious audible part of the difference between speakers today and 40 years ago is not the result of any revolutionary advance in their design, but in the establishment of design targets based on research into listener preferences conducted in the 80s. Today's speakers "sound better" to a majority of today's consumers because they've been designed specifically to suit the preferences of the majority of consumers.
The revolutionary advance is clearly digital sound. Not just "advances in digital sound," but digital sound itself. 40 years ago, digital sound didn't even exist on a consumer level, except as a few analog LPs that had been pressed from digital master recordings. 30 years ago, the first consumer digital recordings were introduced, and a lot of us thought they sounded awful. But within 10 years, they had improved to the point where they had buried analog delivery. Today, CD sales are already trailing digital delivery sales, and the CD is on its way toward joining the 8-track and the cassette as obsolete formats that will someday be collectable objects of curiosity. So digital sound is not only the biggest advance, but it's also undergone the most rapid evolutionary changes.