Your concern is absolutely reasonable and we appreciate your notice. The reason for such inconsistencies is that Contrihub has been created during RailsRumble 2012 hackathon so, as a prototype, it is rough around the edges and bumpy in between. By the time the competition ends (this is now judging period), we will work on refining and extending its functionality.
Projects are currently scored and sorted upon weakness, taking into consideration factors like open and closed pull requests, issues, collaborators, watchers, forks, downloads.