Hi Cary,
Your questuion is not "tough" - you are only a bit impatient to wait for the proper person to answer.
So there are usergroups. In fact, there are a lot more than you can even see as there are many "hidden" ones, too - mainly for beta testing plugins in (also) hidden subforums.
As for the "publicly viewable" usergroups; there are some that you can freely sign up, there are some that you can request membership and there are some that are closed.
This particular "Plugin contributor" usergroup is in fact completely empty for the time being. We are considering populating it along the development of our "Plugin Store" plugin and (possibly) adding some further/additional privileges/forum permissions to its members. Obviously it is a "closed" group and only esteemed members (plugin contributors - as it says) will be members. Similarly to the "Top SketchUcator" usergroup whose members "are known as exceptionally active and helpful as well as highly skilled members of the SketchUcation Community Forums. This is a closed group, new members can only join upon invitation of a group leader".
It is also a "closed" usergroup which means that only forum administrators (like myself) can add new members (see attached screenshot of the admin panel). I hope this explanation is sufficient and clarifies some issues around usergroups.
Also, I am moving this topic to the Corner Bar / Ideas box & board issues subforum (where it should belong).