Aren't most editors unpaid volunteers? There are paid type setters and web people, etc., but the editors who are knowledgeable in the field are not paid except for maybe top 10 journals like Science and Nature.
Yes, the common belief (and it's mine too) is that the gatekeepers like Elsevier use free or low paid experts to pick the good papers and edit them and keep that expensive fee you pay them. Is this only in CS? In my experience all the work was done by free-to-the-publisher editors and what the editors got was listing they were on that journal.
Yea, I brought this up because I have published in a few Earth science journals and that was how it worked in that field.
The editors look at the papers and are the first level of rejections. The ones they think are decent they send to people they think would be good at reviewing the content. The reviews come back (or not, and they send the paper to someone else to review), the editor reads the reviews and, if the reviewer think the paper should be published, the editor sends the reviews to the author for the author to make changes to the paper as needed. The author returns the paper with the edits and explanations for why some suggestions from the reviewer were not followed. The editor now usually accepts the paper for publication and hands off the author to a typesetter that will help in getting the Word doc or TeX formatted paper into the style that the journal wants. This last person is paid by the journal, but in no way needs a PhD in the field or much knowledge of the material he/she is reading.