This must also affect the choice of materials for mains-voltage incandescent light bulbs, and high-power valves. Perhaps one of the reasons for the quartz in 'quartz halogen' (another being that the envelope shouldn't collapse!).
I could have mentioned earlier that a proportion of HV distribution insulators (in the UK at least) have their axis horizontal, particularly at corners in the route. Those with their axis vertical might not be expected to provide so much of a current path in the rain, particularly 'mushroom'-shaped ones.
Chris