Canadian Broadband → Re: FibreMedia.ca - Residential Gigabit Internet

»www.ieso.ca/imoweb/siteS ··· p?sid=bi

Power Companies regulate the voltage continually and in emergency situations as outlined above relatively drastically.
As the load in the grid increases the voltage will reduce ( sag) as the load reduces the voltage will increase. Ohms Law again.
Power Companies keep the voltage within established guide lines by directly manipulating through changing tap positions on transformers or by switching in and out of service VAR resources like Capacitors Banks or Reactors in response to those continual changes in the load and therefore the voltage of the grid. To say power companies cannot arbitrarily lower voltage just isn't quite correct.

That link talks about reductions of 3 to 5%, which is half the 110V-120V normal operating range of applicances. Of course voltage fluctuates, that's why there's an operating range in the first place.