+++ This bug was initially created as a clone of Bug #19239 +++ emacs22-common-22.1-alt2 Some things can be completed in the minibuffer (e.g., filenames for C-x C-f). It would be convenient to have it for man, too: M-x man ...TAB could suggest the available manpages (as bash-completion does).
Use M-x woman for completion, this is documented behavior.