Another version of the same idea: I've read that people who hike really long hours just crawl into their sleeping bags as soon as they get to camp, thus eliminating the insulating jacket.
For those of us who, during the day, like to stop and admire the view (aka rest stop), the thought of completely unpacking to get the sleeping bag out of the bottom of the pack at every stop doesn't sound enjoyable. I personally get cold enough that I need both a puffy jacket and a warm sleeping bag for really cold nights.
I got lots of excellent ideas from perusing Glen's gear list, but that wasn't one of them. On the other hand, I'm in the process of adapting his first-aid list to my own needs in hopes of achieving the same weight.
YMMV, of course!