Yes, I think that the extra weight is from the draft tubes. Probably means a little more down stuffing too. I have them on my Yeti & it seemed like a great idea to cut down on the air movement out the ends (that's why they have them around the neck on a mummy bag, right?!)
I saw a thread right about Thanksgiving wherein StormCrow said that they had added draft tubes to their products. I thought that they maybe didn't put them on the ones that they had made for the supersale, so I contacted them to make sure that they were going to be included. It was worth it to me. I like them and I'm more concerned about the draft/cold than the extra few ounces.