You can't make a crowd become smart commenters by criticizing the way they comment. Instead, TechCrunch should really move to some sort of voting scheme so that the good comments move up and you can ignore the bad ones. I really don't know why more big blog sites don't do this already - it seems like a straightforward win in terms of user experience.
Why can't you criticise (did I spell that right?) your users now and then, when they do that to you on every single post? It's not like you care about offending them anyway, since they are the kind of users you do not want :)
