Sure, that means the structure is utterly ADA non-compliant,but it keeps the little kids out and all but the fittest adults, too - which is the whole point, after all. It's hard to imagine anything cooler than joining the club of children who found in themselves the strength and courage to make it up there.
The treehouse sits in a huge Live Oak at the Peninsula School in Menlo Park. Given the school's progressive philosophy and history, I wouldn't be surprised to find that friends with disabilities get hauled up there on pulleys from time to time. It's a rare place, though, where moral decisions like that pretty much have to be left up to the kids.