Actually, I think it's a technicality on the 'permit'. Any commercial enterprise, regardless of size, or any large gathering of folks that has the potential to cause environmental mitigation, under NEPA, requires a permit. Because we take money for shirts, plaques, etc., I think the FS can say we need one for 10 or 200 rigs. The 75 number is what we came up with to cap the size of the run to maintain small flavor and what I always indicated was the maximum we would have when I submitted for the permit.
That being said, the trail is always open to anyone as a FS route and if coincidentaly 10 - 200 rigs just happened to be on the trail at one time, one could argue lack of permit. But, as Tony said, we do the permit to show organized use to keep the route open.