Why not just add a small negative weight to all articles that come from an address which isn't unique? For instance if someone discovers XKCD for the first tim

Why not just add a small negative weight to all articles that come from an address which isn't unique? For instance if someone discovers XKCD for the first time and submits 20 of them, sure they're great but presumably once you've seen one you could navigate the rest of the site on your own. So add a little automatic downmod to the other 19 submissions because it wasn't a unique site. It would alleviate the techcrunch problem and similar ones without actually banning anything.