Neal,
I will attempt to answer your questions, but these are my opinions, not substantiated in anyway.
1. No.
2. G10's are requisitioned for specific needs. I think its fair to say that the Army needs more than the RN/RM or RAF.
3. If you are going to get seriously wet (from any service) then I'm sure you would be issued with a divers watch. The G10 is a field watch so more of a soldier's watch. I don't know who would qualify for a G10 in the RAF. Perhaps the RAF Regiment or key operational ground personnel.
4. I've seen one non-luminous G10 in about 6 years of looking on the internet so they are out there but very rare.
Those in the military often say that most watches are kept in stores and get signed out to non-combat mates, sort of who you know and not what you do type of situation. Also I'm lead to believe that most soldiers have a preference for G-Shocks and the like and a G10 means nothing to them.
Terry