Simply put, a Commenter is someone who makes comments on something (discussion, remark, observation, criticism). A Commentator is described as a person who makes commentaries or, more often, a person who “discusses news, sports events, weather, or the like, as on television or radio”. In common vernacular, a Commentator is always the latter.

Now, if people are being facetious, or investing in commentary about the quality of the comments of most commenters on web (i.e. the commenter is more interested in the advancement of his or her own platform than in the engagement of discussion or true observation relating to the topic at hand — which can be described as a running commentary of sorts, via several online venues) , then I can see the use of the word Commentators. It should be recognized, however, that those people are now commentators themselves, unless they are making one-time remarks on the subject. Further, their use of the word Commentator in this case in no way changes the actual meaning of either Commenter or Commentator — at least not until the idea takes off enough in vernacular language that the definition becomes changed in formal language.

So, in conclusion, a Comment or Commentary on Commenter quality as Commentary does not necessarily constitute calling Commenter Commentators — except as a Comment or Commentary.

:P