"My dad apparently thinks he's being cheated somehow whenever a program doesn't fill the entire screen"

He's right. They are actually cheating us out of pixels as well. The more wide the screen, the less pixels per diagonally measured inch. At any given diagonal measurement, a square has the most surface area.

That means that at the same resolution, a 19" monitor that is 4:3 has more pixels than a 16:9, and even that has more than a 20:9 or whatever those super wide nesr are now.

Less it more, ignoran... well you all know thow thaat one goes.