Well, my WT BJ is a large, as will the EB XV (when it arrives), so they're a little smaller, but I think one of the big diffs is that I use a compression sack and crank the crap out of the straps, where your photo shows a regular ol' stuff sack.
To Ryan's post, I did notice no internal Nalgene chest pocket, though that won't likely be an issue for me as I usu. carry my bottles in a cozy on the pack or waistbelt. A little disappointed about no two-way zipper, though. (Dumb of me not to check...)