While I have also noticed many duplicate articles, one way the community could try to avoid them would be by making sure that they are posting original sources (as suggested in the official guidelines), and not random blog posts (like the post a week ago).
Yeah, although sometimes it's not particularly obvious. I've noticed a lot of links to a site called http://ontwik.com/ being posted in the last few months (a Google search for ontwik on news.ycombinator.com shows over 100 results). It's a site that seems to take embeddable videos from YouTube, Vimeo and the like and turn them into pages like http://ontwik.com/html5-2/html5-games-with-rob-hawkes-of-moz... .. I can see why people are linking these things up, even though it should be the original YouTube video getting the link.
edit: I have just noticed http://news.ycombinator.com/item?id=2777508 , which AFAIK links to the same URL as this.