Are you talking about the individual counts for a forum or user post counts? The forum post count always reflects what's actually there, so there isn't a way around that. User post counts should remain accurate, as long as the forum is set to count posts.
Hey @Mike - For the most part, I am referring to the overall post count of the forum. My past forum service, I just created a node that was titled, 'Old Posts', and would move any unnecessary posts there. I was just inquiring here to see if there was a better way or maybe even an add-on that kept them somehow .. although, I couldn't find any such thing.