It only makes sense the closer the viewer distance the higher the PPI. I view my cell phone normally at less than 8" away. My laptop at maybe 14" away. My desktop at 30"+ away. For people with less than great vision even 1080P at 24" is pushing things. The places you see larger PPI monitors are in medical situations etc. where people need to be able to get much closer to the screen than normal use to examine high quality images.