Won't deny, since again, PPD depends on your field of view.

Yes, if you shop for "resolution and diagonal size", you may as well shop for PPI directly. This just doesn't generalize to displays overall (see my other comment with a TV example), as it's not actually the right variable. Wrong method, "right" result.

> The threshold for sharp edges is much finer, and the things we put on computer displays have a lot of sharp edges.

And the cell density is even finer. It was merely an example using a known reference value that lots of people would find excellent; I didn't mean to argue that it's the be-all end-all of vision. It's just 20/20.