I speak out of my experience as editor: errors and omissions -- including omissions of citations that would constitute "plagiarism" if uncorrected -- are everywhere in manuscripts, including those by noted scholars with "an impressive recall" for many things. It's just human nature. When I spot errors and omissions, before or after getting them online, I simply correct them on my own. Such corrections are editors' job, not just authors', imho.
Writing for publication isn't an individual job. It's work of collaboration between editors and authors (and sometimes readers, too -- I appreciate their notes when they alert me to errors and omissions in pieces that I failed to identify and correct before publishing them).
Sometimes, I edit very lightly; other times, I edit very extensively; yet other times, what I do is not so much editing as rewriting. That's how things are in publishing.
So, I'd say that Ward Churchill should have gotten himself better editors.
-- Yoshie <http://montages.blogspot.com/> <http://mrzine.org> <http://monthlyreview.org/>