Definitely not just you! What quilts are you using? I tried to get away with a regular width from Enlightened Equipment, but much as I want to love it, I've been forced to admit it's not working for me. I'm looking at Zpacks as a potential future purchase, although I really like that EE offers Climashield models. Maybe Tim can make me an custom wide.
I imagine it comes from the same ergonomics studies that determine the height of chairs and width of airline seats and such. It does seem like an arbitrary choice, though, given that I've never met a single person who actually sleeps motionless on their back the entire night like the optmistic little tent diagrams always suggest.
Jason, that is what I plan to do with a Neoair All-season when I put together a ground setup. For now I use a hammock, which conveniently lets me sidestep the dilemma. ;)
I wish I weren't limited to the Neoair (though I'm sure it'll work out satisfactorily). I think I'd like to see some Exped mats in s/w dimensions. Many people speak highly of the comfort of Synmats and Downmats.