Though I think all of us have probably used a sleeping bag as a quilt, the "inventor" ray jardine, is pretty hard core about how he sets up his sleeping. For him, all his clothes are part of the system. While i would guess most of us have at least some exposed skin. But drafts aren't going to bother ray, because he has his various draft stops, and he may be wearing clothes to boot.

Your feet don't come out because he has a foot pocket in the bottom like an unzipped bag.

Weight savings are a really subjective thing. If you take a really mesomorphic guy in a bag, there comes a point where he is using the bag as a quilt cause he can't zip it up. That guy's quilt will be the same size as a bag. But someone with oceans of room in a bag will be able to trim down a quilt. That is one of the real advantages, quilts are dead easy to make. You can make them with no sewing. They are cheap and virtually disposable. As a result they can be customised to your precise needs.