I believe usually when this happens the admins like dang and tomhow manually unflag the post if they think it's relevant. Which... is not a perfect system, but it works. I've seen plenty of posts be flagged, dead, then get unflagged and revived. They'll go in and manually flag comments, too, to get the conversation back on track. So, I think site admins are aware that this is happening.

Also, it's somewhat easy to tell who is a bot. Really new accounts are colored green. I'm sure there's also long-running bots, and I'm not sure how you would find those.