Well, Josh, I have to be honest: I dont even begin to agree with your premise. True, there is the historical model of the bedroll, which of course helped win" the West or at least helped rob it from the folks who were already there. But I cant even imagine trying to use a blanket for anything halfway serious.
Lets look at an example. Im going camping where I expect to see low temperatures of around 35 degrees. Chilly, but not real cold. I could, per your theory, pack along something like a Lands' End Aircore Blanket ($45), which is made with Polartec 200 and is a nice warm blanket. Now, I happen to have one of these, and it tips the scales at about 15 ounces. And I would need at least two of them. So were close to two pounds.
Meanwhile, my MontBell U.L. SS Down Hugger #3, rated to 30 degrees, weighs one pound, seven ounces. Thats seven ounces less than the two blankets. Plus its warmer because the Polartec pieces arent that windproof, and the sleeping bag is much more resistant to drafts coming up from the floor. One could shave some weight off the blankets by trimming them down to a more oval shape, but then you lose the ability to tuck the edges under yourself. The bag does cost $260, but for its vastly greater performance, I dont think thats bad.
If someone has numbers that make more sense than this, send them on. Otherwise, Im sticking with a sleeping bag.
The 2009 Winter Outside Buyers Guide is now online. Go ahead, get everything you wish you had gotten over the holidays.