http://beta.musicbrainz.org/statistics/relationships has some entries with an explicit "0" and some with nothing shown.

I think it's nicer if the 0's are hidden because it's mostly parent relationships where this happens.

Unfortunately there are a few Recording-URL relationships that aren't being used at all and it would look weird if no values were shown. I'm not sure what to do about that (besides just getting rid of completely unused relationships).