>There was never a planned -100 of the 757, 767, or
>777. The -100s didn't sell very well. Boeing named the
>first derivative of a certain aircraft -200 to just
Not true - There definately was a 767-100 planned, with a 180 passenger capacity. This is well documented. And as others have said, a 777-100 appears to have been thought of as well.
Manufacturers don't just start on 200 because it sounds cool. Usually the suffixes denote the stretching or shortening (ignoring the 737 middle generation) - A -200 model is usually shorter than a -300 for example. This is just to make room ahead of time for a shortening, if there is a demand. One example is the A330-100, that has been talked about but then was dropped as well.
Of course the A32X series has its own strange system...