Is there a case for having the latest replies to a posting put on top of the stack and pushed down? Some well known sites do exactly this. In fact this procedure is followed where the newest question is always at the top.
I'm sure there are advantages and disadvantages whatever method is used but its a well known fact that postings get read more often when looking at the latest contribution.
Ideally, when you click on a thread it would take you to the most recent post (whether they put that at the start or end). I find it easier to read a conversation in chronological order, myself.