Apple's is based on the typographic convention of 72 points per inch, thus text on a Mac screen would be drawn the same size as it would print.
According to Wikipedia, Microsoft's 96 is apparently based on screen text being viewed from a different distance than printed text, so they use 96 ppi to account for the difference, which also gave them more a few more pixels with which to draw characters. Apple had to draw a 10 point character 10 pixels high, but Microsoft could draw a 10 point character 13 pixels high, giving them more to work with.
> Apple's is based on the typographic convention of 72 points per inch, thus text on a Mac screen would be drawn the same size as it would print.
This would be true if the displays were also 72 dpi, which they are not. DPI in Windows can be set manually. Mine is set to 84, based on the handy on-screen ruler in the settings page. If I view a document in Word's print preview at 100% zoom, and stick a printed page on my display (via static electricity, try it) next to it, they match exactly. Very handy for printing over a page with existing content (paper with preprinted corporate borders, headers).
I think the Mac displays used to be, at least at the maximum size. I vaguely recall Mac monitors being somewhat "lower-resolution" than same-size Windows monitors, just because of this. Maybe it was Mac laptops? Not sure. Certainly the original Mac 128 was fixed resolution.
"built-in display was a one-bit black-and-white, 9 in (23 cm) CRT with a resolution of 512×342 pixels, establishing the desktop publishing standard of 72 PPI"
ImageWriter prints were 144dpi, and you could verify thtat the system was WYSIWIG by holding a print in front of the screen. Also, Mac OS graphics used 1/72" pixels for years (with various hacks added soon in order to support the LaserWriter's 300 dpi)
Windows (initially?) had separate notions of device pixels and logical pixels (dialog units?) that allowed for some resolution independence. Its most obvious disadvantage was that it was not simple (neigh impossible?) to know whether two parallel lines you drew looked equally wide.
ISTR that displays also squawk their DPI over EDID. I say that based on experience fiddling with point sizes to get Glass Tty VT220 working right on several different displays; but of course you can also change the dpi with a magic xorg.conf setting, command line option, or xrandr.
The same reason why Apple has not changed iOS devices' aspects and "virtual pixel count" since day one. Android did allow random resolutions and screen aspects, and look at the mess it has caused.
