While I pretty much agree with you, and the water heater advice is great, I suspect that a decent part of that $300 jump in the winter is because the temperature of the water entering your home during the winter is much colder than it is in the summer (a.k.a. it costs significantly more to heat the same amount of water in the winter than it does in the summer).
Probably not. Water entering the house comes in below the frost line so the pipes don't freeze in winter and the ground temperature below the frost line is pretty constant year-round. There is a small change, but the water coming out of my cold faucets is almost the same temperature whether is 100F or -25F outside.
