There's definitely a little more room at the exit rows - certainly not A321 style room but I think it's the same on the A320 as the A319 with a couple of inches extra at the exit row(s)

I wonder is it that the A320s with the old seats had rows 10&11 as the Exit row and the newer spacesaver seats have Rows 11&12 and because they don't know this far in advance which aircraft will be used they just mark all 3 rows as exit rows ?

Just my theory but seems logical I think ?