Why set bias so low?

I just picked up a really nice 210-65 from an ad in the local paper. All's well w/ the amp - I pulled the chassis just to give the pots a good cleaning, and set the bias per the instructions here. Anyway, that got me thinking - why is the bias set so low on these? The target plate dissipation on an EL34 would generally be 18.75 Watts, which at a 700V plate voltage would be 27 ma. Through a 3.9 ohm resistor, this would be a measurement of around 100 mv, yet the target in the instructions was to shoot for a quarter of that.
Most amps sound like complete crap if you bias them this cold - why is this different? Does it have to do with the cathode connected transistor?
Thanks,
Steve

Never got an answer did ya? Probably sold the amp, it traveled here and there then, if this planet is as small as they say, it very well could be the amp I picked up recently.