Why does stereo equipment need a grounding source at the receptacle?
For the same reason any piece of equipment would require a ground- to eliminate the shock hazard should the case become energized.
Is the grounding an absolute must for semi high end stereo equipment?
Don't see what "semi high end" has to do with it (or even what it is). It's up to the manufacturer to design the equipment so that no shock hazard exists and if they can do that without a ground and still pass laboratory testing (such as UL) then they won't need a ground.
And last but not least why do some manufacturers of equipment claim that without proper or good grounding the equipment will not work.
Got me. They shouldn't be relying on the ground for any more than safety. Maybe they are trying to scare the customer into doing the right thing.
-Hal
