Servo circuits are basically an outgrowth of the negative feedback circuit that takes into consideration the actual movement of the driver(s) itself. If the driver is "throwing" too far, the amp cuts back signal to correct this. If the driver is not "throwing" enough, the amp sends more signal. As such, the amp is trying to correct for non-linearities in both the signal and the driver(s) / cabling being used.
The only problem with this is that the servo system can only try to correct a problem after it starts to occur. As such, servo's are always playing "catch up" and can't correct errors before they happen. Having said that, it is somewhat true that combining an active servo-amp with active equalization can give a speaker system a form of "psychic ability" i.e. ability to correct a problem before it occurs. This is due to the fact that the engineers know how the driver / amplifier combo is going to react in a given situation and can program in corrective EQ to balance that out. This is one of the theoretically "great" things about active speakers i.e. the reproduction / amplification chain were all designed to work as one unit. Obviously, room acoustics and speaker placement do vary, so good engineers will give you some adjustments to work with in any servo or active speaker type of installation. Sean