Analog stretching doesn't affect picture quality in a perceivable way -- you did that to adjust the picture everyday with CRT monitors, and they're meant to be used like that. What the monitor does when it's displaying at full-screen width sub-320-px resolutions is not "analog stretching", it's just a more "relaxed" way of placing the pixels of every scanline. If anything, you need to worry when the picture's horizontal res. is bigger than the number of "TV lines" your display is capable of, since the pixels start merging together. But not when it's smaller.
Stretching or not, it's just a matter of semantics. The horizontal size of the picture is changed. Squares becomes rectangles. Everything looks fat (or almost).
Arcade games that use 256, like NES and SNES games, looks nicer with square pixels. Proportions look right.
It just looks better.
If the artists didn't care about the "stretching", how come can you say that whatever object is not looking the way it should when "stretched" a bit?
Because to compensate the "stretching", the artists needed to go out of their way. So, if most artists didn't care, the way it should look is
without "stretching".
What I tried to explain to you is that, 'cept for your mandatory anecdote, they indeed were ultimately intended for RGB, even for those few cases without the required RGB output.
You can use the same argument to say square pixels were their true intention, considering the graphic proportions in a lot of games looks right only with square pixels.
I really doubt (most) artists made a conscious decision to draw differently either the system were capable of display a horizontal resolution of 256 or 320.
I know there are exceptions, but overall square pixels looks better.
I just don't like when the graphics looks "fatter". But I can tolerate looking "taller".
And because, for most instances, that's the way you keep the intended pixel aspect ratio. And also, because they have better monitors than yours for displaying sub-320-px-width pictures, it seems.
I'm more like a collector, so I'm very used to all kinds of CRT monitors.