While it certainly makes sense for an airline to keep certain seats for its own own frequent flier program members, I am not sure that this approach would work for paid tickets. If that were truly the case, how could a ticketing agent (travel agent or another airline) rely on Apollo, Sabre, etc. to find available seats for a specific booking class? I thought the whole purpose of these reservation systems is that any agent anywhere in the world can book and reserve seats as long as the reservation system shows availability in the desired booking class?