Generally, people don't post personally identifying information and I'd encourage them NOT to. Sometimes though, they might make a thread talking about their personal life (something that happened), OR like here, maybe they've made a thread about their website. They might have added their photo to a "post real pics" thread. Beyond that, most people won't be leaving much info about themselves behind. That's why they use a pseudonym afterall.
Webmaster forums are different. You might have to actually block their website or something to ensure that there are no links/mentions of it anywhere.
Let's face it, if your 5,000 post boy/girl has started a lot of generic discussion threads that anyone could have started, you're talking about possibly deleting 1,000s of posts by other members. How is that fair? Those threads are not in any way personally identifying. Anyone could have started them.