Why are most High End Amps class A

There's also Rod Elliot's explanation , if it hasn't been mentioned already.

http://sound.westhost.com/class-a.htm

Lot's of other articles/projects too.

I also have a Mark Levinson amp that has that AB class sound. To me the push-pull method has it's advantages such as clarity, efficiency, and low distortion. I've had this amp for ten years and I have enjoyed every minute of it... until now. Reacently I noticed that while the sound has the above advantages, it seems to lack depth and realism. A tuning fork has the same advantages as a class AB amplifier, but would you rather hear a musical piece played with multiple tuning forks, or musical instruments with their own distinct overtones. Class A amps have more distortion than class AB, but perhaps it's that distortion that gives class A amps their flavor, and realism. Anyway, that's my two cents worth.

Kirkus, perhaps Nelson Pass refines Class A amplifier design to a higher level, but the fundamental Class A characteristics that I currently experience, wrote about in this thread and elsewhere is the same thing that Redwoodgarden and numerous audiogoners have described. These characteristics set this particular design so far apart from others that I can have the realism of music at home rather having to severely limit myself to just live concerts here and there. Secondly I did somewhat follow the engineering discussion here and on the internet. But there is only so much the oscilloscope and math can help you assess reality. Ultimately it's the human ears that decide one way or the other. Thirdly Levinson ML2/3 were made late 1970's and early 1980's. Don't you think it's too risky to recommend people buying equipment that old? Finally, the newer Levinson amplifiers to me have their strength in precision and clarity, and that was the basis for my entry into the audiophile world a few decades ago. It really was a fine start, considering what's offered at the national chain stores.