I'm guessing this may be because the new file was added after r37404, but the file registering the extension (and providing the revision number) wasn't changed at that time, which means the most recent revision of *that file* is still r37404. Special:Version doesn't really report the most recent revision of the extension as a whole, but that of the setup file (IIRC).
Indeed. It would be much nicer if it could report the *directories* revision number. Does SVN have a keyword substitution for this? Does SVN allow scripts/plugins for this type of thing? That would by quite useful.
-- daniel