For me, the arm holes are great for venting and for getting rid of that initial sensation of claustrophobia. It's also easier to zip up the bag with your arms out, and to grab things at night without having to unzip the bag. While I love the freedom, versatility, and low weight of quilts (I have both a 20* and 30* from EE), I was always colder using them, especially since switching from a tent to a tarp, and not wanting to use any pad other than a Z-Rest. The Mobile Mummy 3-season not only solved my coldness issues, but in particular they, ExPed, and ZPacks place their zippers down the center of the bag (instead of on the left or right) which is the best location for a zipper as far as I'm concerned. I initially went with the Mobile Mummy because it was the cheapest of the three I could find at the time.
I do agree with you though: I wouldn't sleep the entire night with my arms hanging out either.