I've been bombing around backcountry.com looking at the Big Agnes bags lately. I'm intrigued by their idea to not include fill in the bottom third and use a pad sleeve instead. It looks like they're able to cut a good deal of weight out by doing this.
My question is this: is this system sound? It seems like it to me, but I can't figure out why the rest of the sleeping bag manufacturers aren't doing it if it works. I would think the other high-end makers like feathered friends, marmot, etc. would be offering a bag with a pad pocket instead of bottom insulation if this worked.