Heck some heavyweighters aren't prepared. I have seen folks come into the shelter so exhautsed from toting 50 lbs in the freezing rain all day they were hypothermic and there heavyweight gear wasn't all that warmer than mine even though it weighed 3x as much.
I would rather set up my dry bivy sack and quilt under a well pitched 1 lb tarp than crawl into a wet 3lb sleeping bag in a soaked 6 lb tent.
I realize that there is apoint where going lighter does cut margins of saftey and comfort and there is certainly is a point of diminishing returns as regards weight and comfort, but decent judgement and some experience is a bigger part of the eqation that weight.