I don't know about the post count but I know a thread I replied to using the quick reply has the black dot on it and is showing in my CP. Although I don't know if it is showing up there because I posted to it, because I had subscribed to it yesterday but then today quick replied to it. But it does show the black dot on it.
I will keep an eye on my post count and see if it goes up next time I use the quick reply.
Mike