They use the 640x200 EGA mode, that way they only adjust in one dimension.

Whoops, I was afraid I'd get that one wrong.

The version I had was the 16 colour version of SQ4 and it had a Hercules Monochrome driver.

Interesting, I wasn't aware of that since I only bought the VGA version. I did end up with both the EGA and VGA remakes of Space Quest I though, but I'm sure I didn't pay much attention to the sub-EGA support.