Can that be true? What a disappointment... you British are supposed to be the most animal friendly people in the world - a "sterotype" that I as an Anglophile happen to hold very dear...
It looks like a very big, natural enclosure As for keeping the bears inside at night-maybe it's to guard against the (although probably slim!) possibility of a bear getting out and going walkies?
I know this is a really old thread, but just to clarify, the animals at Dartmoor have access to both their outdoor enclosure and their house 24/7, the only exceptions being in high winds and storms where there is a risk of trees hitting the fences.