As far as the XL1 vs. S1, The XL1 has a longer barrel and is more end weighted. S1 has a shorter barrel and is more balanced.
As far as the 13 model vs. 11-12 model, the composite barrel on the original XL1 (white barrel) had a shiny/slick/smooth finish. Of course, after being used it gets roughed up. On the 13 model of the XL1 (yellow barrel), the finish is a flat paint with a little grip to it. I don't think the weight or structure of the bat has changed. Remains to be seen whether or not the paint makes a difference.
In theory, the flatter, grippier finish, should allow for more backspin on fly balls and possibly..... possibly allow the ball to stay on the barrel a millisecond longer, possibly allowing for a greater trampoline effect off the barrel. This is my opinion only, not something that Easton is promoting.
In a real world situation, none of that probably matters much.