I think it's a good thing. When a guest posts, the notice gives you continuity.
Otherwise, you might have 5 posts by guests, and no notices until a member posted.
One supposes if anyone is interested enough to join a thread, they'd like to see it through to its conclusion
I always enjoy hearing what a guest has to say. Just because I normally disagree with them, there's no reason to suppress the whole "free speech thing...."