Some of those files may have been named during the days of DOS 8+3 filename limit. Better keep an old filename than break a lot of links.
Also, some people who first learned computing in the DOS era keep using shortened filenames out of habit, even if it's not always capped at 8 chars. (The site seems to have several files whose names have been abbreviated to 9 chars.)
I know that's not a big deal, but being a fan of ... well, I'd say "semantic URLs" this always hits me square in my face! Why not use "/commonsense.htm" or "/common_sense.htm"?
And after looking at http://www.constitution.org/tp it gets even worse ("/amercrisis.htm" etc.)