Bah. Humbug.
I've been to a lot of national parks over the years, and only VERY rarely have I even seen rangers. Most of the services NPS visitors encounter are run by outside concessionaires. This includes the gift/souvenir shops, the restaurants, the hotels (for those that have them, such as the Grand canyon), and a bunch more. I only remember interacting with actual park rangers twice -- once at Casa Grande in Arizona (which is actually a national monument, not a national park, but it falls under the NPS), and once at the Jefferson Arch in St. Louis.