Currently, fink cleanup --help says that at least one flag is necessary to specify an action. The patch corrects the help message to say that --debs --sources is the default. The patch is against CVS HEAD, but it applies cleanly to the current fink version 0.29.21 as well.
patch against fink/perlmod/Fink/Engine.pm
I've submitted this patch as a pull request on github:
https://github.com/fink/fink/pull/12
The pull request has been accepted, so closing this tracker item, too.