I'll tell you. Around 200 editors who can work anywhere they choose plus all of those named in the category and higher up the category tree. The answer is still around 200 .
Editors' names appear at the bottom of categories for one of two reasons: they have permission to edit only in that specific category, or they have wider permissions but a special interest in that category. Those with wider permissions may be listed higher up the branch as well, or they may be one of the many editalls, cateditalls, meta-editors, catmods etc. There is a list of them here: http://www.dmoz.org/edoc/editall.html NOTE: For reasons I have never understood, the "Edits" column at the far right is usually completely inaccurate, so I strongly advise ignoring it.
Can you show any kind of evidence for at lest that? Last time we saw monthly reports editors where making about 1/2 listing per editor monthly, at lest they where making minimum norm of a single edit in three months.