I'll let someone else (who has actually bothered to look at the source code) speak about the details, but I believe that the major factor you're forgetting is c

I'll let someone else (who has actually bothered to look at the source code) speak about the details, but I believe that the major factor you're forgetting is comment age. In any event, the best general advice is not to worry too much about the karma mechanisms, and just try to make the kinds of comments you think contribute best to the discussion.