When I was growing up in a house in Ohio, I noticed our roof rarely remained iced-over during even the harshest winters. Massive icicles would form from the edge of the roof to the ground, however. I found out later that the cause of all this was not good.
If a roof does not collect snow or ice during winter months, the cause is most likely poor insulation. The heat from the inside of the house is constantly deicing the roof, causing streams of water to form large icicles as they drip down to the ground. Poor insulation means higher energy costs.
If you have to do something about deicing your roof every year, at least you know the insulation is doing its job.