I don’t think the article directories rank all that well. They have high PR probably because they have a lot of links. Maybe google sees their (article directory’s) content as being more relevant and “worth-ranking” than the original source or maybe the ezinearticles that rank well were indexed before the original? Who knows?
I really enjoyed reading that article as it has cleared a lot up on dup content for me.
I think article marketing in the sense of taking already published content from your site and posting it on another site is a pretty silly idea.
However, writing a unique article and having a webmaster publish it exclusively on their website in return for a few links may not be so silly.