History of audio:
First we had electrodynamic speakers. They were expensive to build but they sounded better. As soon as it was practical, the industry moved to permanent magnets. It was not about sound, it was about the money.
Then came the transition to transistors. Suddenly no filament circuit needed (cheaper power transformers) and no output transformer, plus loudspeakers didn't have to be as efficient (reduces cost by about a factor of 10 to be less efficient). Again, cost to build goes down; the industry nevertheless gets to charge at least 90% of what they did before...
Then the transition to digital. A lot cheaper to record and produce; the industry got to increase profit margins while selling the public the same tunes they had before.
Now comes class D. Again its a lot cheaper to build so the profit margin is tempting as again the retail prices are only slightly lower in comparison to the cost of construction. Like other technologies class D is still evolving at its introduction so we've seen older class D amps fail to become classics.
The flip side of this rather cynical viewpoint is there is a fair amount of pressure for the industry to go to class D. The semiconductor industry really doesn't want to make linear devices as much; class D has taken over 'midfi' and when competition is making fairly competent amps that are a noticeably less expensive, then others have to get into the game....
With any power amplifier its all about the distortion the amp makes and what distortion it does not. That's why tubes are still around- they make less of the higher ordered harmonics that the ear finds to be unpleasant and also to which it is keenly sensitive. So the trick with class D is to make them well enough that they don't make the traditional colorations of solid state (bright, harsh) and somehow sound like music.
