I don't think that is accurate, as my companions OFTEN say they are "just so tired" when I still have BOTH short rests available... I swear sometimes they say it when everyone is full health, plenty of spells and barely have started the day. I also don't remember them basically ever saying it during act 1 and most of act 2, but that was around the time Patch 1 came out... I'm wondering if they added triggers for those lines to subtly convince people to spend more time in camp to progress some of the story - something to combat the fact that a lot of people seem to be missing lots of story by resting infrequently.