This is true, which is why I'm hesitant to make my pages look trashy/spammy if they are not going to be re-blogged anyway.
Maybe on the chapter titles or last page would be appropriate for the url, but not constantly throughout on every single page. If I find it annoying when I'm reading comics then I'm not going to subject my readers to it. (especially those authors that will post their urls all over the page or even right on the panels or even over the text, that's just makes me stop reading at that point)