There are a bunch of different, sometimes related, sometimes not, topics running around in this thread.
I few thoughts:
- Ski areas often rope off and close areas within their boundaries for safety reasons. They do what they can to enforce these restrictions against everybody, whether they have a ticket or not. Of course, it's a little harder sometimes to stop someone who doesn't have a ticket, if your prime enforcement action to pull a ticket.
Similarly, the Forest Service likes the ski areas to warn people who leave the groomed/patrolled/lift-served areas. The government is no more excited about sending out helicopters to rescue people than the ski areas are.
- The general terms I quoted should be in all ski area permits. They are among the provisions in the form that the Forest Service supervisors aren't supposed to modify.
- It would not surprise me if some ski areas have, in practice, violated the terms of their permits by attempting to restrict access to non-ticketholders. They're not necessarily just being bad guys: it may surprise you, but a lot of the people who work for the ski area may not even know what the permit, or the law, says.
- The whole topic of going in and out of the boundaries of a ski area gets pretty complicated. A lot depends on what's on the other side. If, for example, it is a National Park: the National Park Service can be hostile to people paying to ride lifts and then using National Park land to ski. It's sort of ironic, but they may allow people without lift tickets to cross the boundary, and try to stop people with lift tickets. Incidentally, the National Park Service and the Forest Service are about as distantly related as any two federal agencies: they're under two entirely different cabinet-level departments: Interior and Agriculture, respectively.
Even if the border doesn't have a National Park on the other side, it may have a wilderness area. Some parts of the National Forests are wilderness areas, which are intended for different uses, and the Forest Service might restrict skiers from crossing from a ski area into a wilderness area (even if it is still in the same National Park). Various other concerns come into play: watershed and habitat protection, tribal rights, etc. Also, there are often chunks and pockets of private land inside of National Parks (as a ski area developer, you want your base area in one of these). Some are mining claims that predate the establishment of the Forest. Some are railroad landgrants (those one-mile-square checkerboards).
- The ski area does own the improvements it builds at the ski area: not only the lifts, but the buildings. Theoretically, I guess they could check lift tickets at the bathroom doors. It would be sort of amusing, anyway.
- Forest Service permits restrict the ski areas and other permittees in a number of other ways. Improvements have to be approved. If a ski area fails to keep up and improve the ski area, it could lose the permit. Owners of condominiums that are on permitted land may be required to rent out their condos a certain number of nights, and may have to pay a nightly fee to sleep in the units they "own."
- I don't really know about ski schools. Note that, though the permit holder can't keep the public off the land, it does have some exclusive rights: somebody else can't build a lift in the permit area, for example. Also, there's a public good in keeping out charlatan ski instructors. An analogy: tennis courts in city parks are open for anybody to play on, but the city might restrict instructors to those it approves. It seems that some sort of process for approving and authorizing ski schools is consistent with the principle of the permit, though I don't know the actual rules or practices are.
- As noted, this all relates to Forest Service ski areas only, which are mostly in the West. Some western areas are wholly, or partly, on private land too.