With the exception of class A airspace Class B, C, D, E & G airspace either can or does start at the surface. We (modelers) fly in one of the designated airspaces which are the subjects of this poll.
Read the applicability part of Part 91. It says it applies to each person aboard the aircraft. Our aircraft does not have people on board so part 91 does not apply. The FAA act of 1958 says the FAA has authority over navigable airspace. Navigable airspace and its boundries are not part of the airspace definition but is a major part of Class G airspace. However, there is part 77 which governs obstructions to airspace.