When you post on someone's topic, do you expect an acknowledgement from the person who started it? If you don't get an acknowledgment, would you stop posting on any other other topics by the person?
I personally don't expect an acknowledgement from anyone. However, if I had spent a lot of time on a reply on the initial thread, I would keep my replies shorter on subsequent threads in most cases, if I remember the poster, which I usually don't.
Maybe I need to google discussion forum etiquette.