On the one hand more refined knowledge allows a better product at the same or less cost. (you can get a new 100WPC stereo receiver today for $100, that was impossible 15 years ago)
On the other it allows for cost savings by decreasing the extent of over-design. The designers can target a desired life-span much more accurately today, whereas 15 years ago, there predictions had a greater degree of inaccuracy so they added in more over-kill to err on the safe side.
So my opinion is that some of the older electronics can be superior to the extent that they were over-built, but a well built modern amp can certainly match old gear.