Guess what other obscure old system used rectangular pixels? The IBM PC.

CGA and EGA used resolution modes that were multiples of 320x200 (PAR 6:5). VGA's 16-color hi-res mode was the first to support square pixels at 640x480, and it would become a standard for years to come because TempleOS and Windows used it (you can even force Windows 7 to run in this mode!)

The NES and SNES had PAR ~~16:15~~ 8:7 (oops) (which is often ignored in emulation), and so did the most common NTSC DVD-Video mode (none of the commonly used ones had square pixels but you only really notice it with subtitles - you cannot correctly display them at native resolution on an LCD).

And that's just the successful systems I know off the top of my head.

Soviet personal computers failed for other, obvious reasons. They struggled to copy the latest chips, and the economic incentive was minuscule despite the government's investment - very few people could afford a computer in the Eastern Bloc, and they could not be exported due to patent infringement and being years behind. The economy collapsed after USSR broke up and nobody wanted to invest to rebuild the industry.

That being said, people in the Eastern Bloc were very resourceful with what they had (mostly clones of Atari's 8-bit home computers and IBM PCs). A blind person from Czechoslovakia made a speech synthesis sound card for an IBM-compatible PC, which functioned well enough to allow him to be employed as a full-time programmer. At least one of the three exemplars works to this day.