Perhaps it's the enthusiasm of the fans rather than the vidworthiness of the source material? It would be interesting to plot that actually: fandoms with shiny visuals versus fandoms with really enthusiastic fans, with the goal of finding out whether those fandoms which had both would be the ones with the most vids or the best vids...

Funnily enough I downloaded both of heresluck's Due South vids last night before I even saw your comment. I really enjoyed "Out There" (a different and more thoughtful look at the main character than I'd seen before) but "In The Mirror" didn't really grab me.