I'll go ahead and jump in to help straighten out or confuse the situation as best I can.
First of all we have power to 2 out of our 5 coops.
the power is used in the layers coop (misc full size breeds) on a timer for adding supplemental light to aid the girls laying schedule, and to help us see when we go looking for eggs. its light is aimed at the water to keep it from freezing. 5 birds from this coop (including a naked neck) are currently roosting outside of their own choice.
the second wired coop (silkies, banties, quail, and full size breeds)has heat traced water pipes and lights (also has remote temperature sensors but that's another story). these water pipes have a cord run along them that is connected to a thermostat that kicks them on at 35 degrees. these pipes are wrapped with insulation and pvc pipe cover to keep the girls from pecking the insulation it also keeps the heat at the pipes. basically both coops are wired for my wife's convenience so she isn't hauling jugs of water back and forth at all hours and can see where she's going in the dark (arnt I good to her).
our 3 coops without power (mallards, misc breeds of ducks, and turkeys) have no supplemental heat or lights added just deep litter on the ground and water buckets that have to be filled several times a day and ice chipped out (not so nice to her anymore am I).
Last night our power was out for over 2 hours, but our flocks are climatized to the temperatures so it wasn't a problem. Its currently 1 degree fahrenheit outside but inside our insulated (yet ventilated) coop its 25. Mind you thats the breeders coop they are spread out and segregated yet still manage to raise the coop temp by 24 degrees just by their body heat.
So do coops need electricity? in my opinion only for the humans convenience of checking for eggs and chipping less ice buckets