I have the feeling the regions are the same since the EGA's 620x200 (and hercules mode!) days of windows 3.x for almost all operating systems. Some window managers have updated it a bit but if you look at the increase in pixel density (640x480 on a 14" crt is 57ish ppi, and that is being very generous, vs my home display of 110ppi and the retina displays with 200+ ppi) I get the idea the regions have stayed the same in pixel size despite display scaling and such.

Or we all go (back) to tiling window managers and get rid of all the resizing with the press of a key, or even no press.