Places of work, schools etc can have firewalls that block sites without swear filters or stop people going onto the messageboard if it has swearing in post titles (I recall that giving people problems at wotmania, where words that weren't caught in the swear filter were enough to be blocked by school networks, "sex" for example stopped someone, Tim it might even have been, from going to the Comm boardif it was in a post title)

Basically the difference is that the former is much less likely to stop someone being able to access the site, which is probably not a bad thing if people want the site to survive and grow