I think sometimes is just a case of not thinking outside the box - It is a little harder to visualise a batten at 45 degrees still allowing that wing shape in horizontal section. I also think (the guys in the photo)are pursuing another "constant draft" school of theory, in which case maybe the " hook" at the top edge of the sail that results from the horizontal batten is like a end plate/winglet type deal, justifiable if you have deep draft at the top to minimise induced drag, (the vortices that form as the air spills over the top, instead of going the long route and generating lift.
Personally, I wouldnt mind trying a sail like that on my square. (Anything is better than what I've got, tell the truth)
I guess it is the same kind of unwritten code that makes drag racers go crazy for another 10% HP instead of taking off 10% weight.