I have seen that chance here on HN, which is honestly one of my biggest gribes with the site, everything that is positive is destroyed completely. You can see that with the commentors who used to be found here often (patio11 especially) who are now only around for a few specific threads (but somehow magically there when the threads call for it).

However I am sure it wasn't 9/11 that did it, because I wasn't really on the internet then, and HN didn't exist.