Question about Aspect Ratio

[doko]

Can someone explain why the render resolution doesn't match with the aspect ratio of what is actually displayed? 
From what I know, almost all PS2 games are supposed to be at 4:3, and that seems to be true by pixel measuring the actual PCSX2 display window. But the render resolution of most games is usually 512x448, which doesn't match any kind of conventional aspect ratios.
This causes some problems when taking native screenshots, since the screenshots are taken using the render resolution, making them looks squashed in comparison to the real PCSX2 window.
Is this kind of behavior normal? Do I need to scale the screenshots manually using image editing software?

[Red_Tv]

Same for SNES.
The internal resolution of the SNES system is 8:7
I think the reason for that is that game developers just wanted to make the best graphic possible
the more pixels the better graphic is
until this day people argue if you should play those games in 4:3 or 8:7

for more informtion:

https://www.youtube.com/watch?v=ssluTgfkdlg

[doko]

Thanks for the video, that was a really interesting watch and it shed a lot of light on this confusion.
So how would you go about "fixing" the screenshots AR back to 4:3? Which kind of scaling algorithm (blilinear, bicubic, nearest neighbour, etc.) would produce the most "faithful" representation? The video seems to imply a bad algo could produce image with artefacts.