I think that it should decrease the post count only for posts that get deleted. If the user or the mod does this, it's just as significant, because the post is gone.
Once you've cleared the last frontier by a significant amount, you're home free.
Yeah, but what if you throw an Easter Egg style rank in there for people with a ridiculous amount of posts? (Like I will
) Then if their posts get pruned away, they suffer.
I think pruned posts should still count, because there was still a valid post there, even if it is gone now. And I know I would be pissed if I signed on one day and my post count was tiny.
I do think that Post count should be something that an admin can edit in a user profile, although that might be a future feature. :p