Why are most High End Amps class A

When did audiophile's start to worry about the electric bill
There are some great A/B Amps but they are not great because they are less expensive to operate or that they cost less to obtain.
To think that way is to say a Honda is better then a Ferrari
because it gets better gas mileage.
I find Class A amps to sound better then the Class A/B or D that I have heard.
This hobby is about SOUND nothing more and nothing less.

Bombaywalla - not only bias but also gain (before feedback)is different between class A and AB. Class AB requires much higher gain (usually about 10x) to linearize output transistors with deeper negative feedback. Large gain causes amplifier to overshoot (and even choke) on fast changing input (pulse) since it is unable to feed signal back in the same phase (delays the signal). This is called Transient Intermodulation Distortion and was dicovered in 1970. Before that first SS amplifiers had excellent THD and IMD but unpleasant sound (overshooting introduces odd harmonics).

Using different classes of amps for woofer and tweeter is fine if we can guarantee that phase shift is the same.

Most amps are NOT class A, but AB

Kijanki, could you please explain about the phase shift in a bi-amp setup? Are you saying that different amp has different timing as to when the music is projected out?

Spatine - I've never had bi-amping setup but noticed that people, most of the time, use identical amps for that. Absolute phase should be the same unless amplifier inverts the phase 180 deg - easy to fix by reversing speaker wires. Problem starts when you get amplifier from different family. My amplifier, for instance, is a class D creature based on Icepower 200ASC module from B&O. Data sheet for this module shows +40deg phase shift for all frequencies (0-20kHz). I'm not sure what to think about it. Rule of operation is different and this amp shouldn't perhaps be bi-amped with an amp from another family.

It would be cool though, to use class D with its excellent power, dynamics and bass control with small class A amp for the highs. I'm afraid that harmonics would add improperly and sound would be strange.

Standard (class A, AB, tube) amps might have slightly different absolute phase shift (and different interaction with the speaker) and I wonder about using different amps (or different family of amps) for bi-amping.
Had anybody done that?