I just checked what is easily available to me: v7 calls them sections in intro pages, but chapters in man(1) and man(7).
Celerity Computing UNIX (looks like a BSD port) calls them sections in intro pages and man(7), but chapter in manv(7) (dtroff version of man(7)). SunOS 4.1.1 calls them sections everywhere. HP-UX 11.11 calls them sections everywhere. Given the changes it looks like you are not the first person to note an inconsistency here, but I see a majority calling them sections and getting rid of the term chapter over time. Now all of the above is commercially obsolete by now and Linux dominates, but I don't see a good reason to break an established term and instead suggest to follow the above and s/chapter/section/g. Michael
