@ Mina
The BSA high adventure base at Philmont, New Mexico has the same rule. And while I had my private doubts about its effectiveness, we as a crew followed in. My wife did know a kid in high school who woke up while camping under the stars in Yosemite to experience a bear licking his face.
I took a 30 degree bag to Philmont and also took a down sweater in case I needed to augment the bag on cold nights. There were a few mights when I needed to put the down sweater as soon as the sun set but mostly I waited until after dinner. And while my normal practice is to sleep in most of my clothes on cold nights, I switched into an base layer bottoms and tops. I also have to remind my Scouts that if they get cold in they can among other things 1) put on their rain jackets and pants and 2) get up and make a hot water bottle (operating the stove under adult supervision).
I would guess the NP policy is really to protect the bears from being habituated to associating humans with the scent of food.
