I am not sure about that last post.
First off, not every grounding method uses "green wire". All grounding I have ever done I have used uninsulated copper.
Not having a large piece of metal on your roof most certainly is a fire hazzard. About 10 years ago our large antenna in our attic was struck by lightening. It was not grounded. It traveled through all the Coax in the house, burning up most of it, blowing out two televisions and starting three fires in the house. They were quickly dealt with by the wonderful fire department, but what if no one was home to see what was going on. What if it was in the middle of the night and everyone was sleeping?
What would have happened if the system was properly grounded? Who knows, but it probubly would have made the situation a little better.
Unless you want to replace that switch on your roof in a short period of time, I would suggest getting it inside the house or at the least under some protection from the elements. Weatherproof units in the elements does not mean it will last as long as the same unit under some protection out of the way of the elements.
Even if your house is pre-wired, you most likley have a central area with all the COAX from each room comes together. That would be a perfect spot to put a switch.
Please let us know how your conversation with Directv went.