Michael, that is an astute observation, especially if you did not already read about it here. Improving the performance(while reducing the weight) of outdoor gear is like improving a system of systems, of which the sleep system is one. It has requirements for wind protection, water repellency, vapor management, conductive and radiative insulation, etc... and of course a combination of durability and yet low weight. My system is comprised of a ground sheet, tent, sleeping mat, bivy sack, sleeping bag, and the layer(s) I wear to bed. The sleeping bag is only a small and light part of the total system; in fact I could probably do without the 1 lb bag at all in a pinch.
I suggest you read the forums for more info..