Well, speaking from the point of view of someone who has been a noob on a number of boards, it is awkward and intimidating going into a new board and being expected to post when you feel out of place just getting your first post out there. Posting a lot is daunting.
I don't know if it is an option on this forum system, but I have been on a forum that gives you the option to post in an "introduce yourself" thread instead of meeting a post count to give privileges to post in certain boards.
I'd be fine with requiring a certain number of posts before allowing starting a new topic on B/S/T, but to reply to a thread I think it would be nice to offer newbies an alternate plan, we got a pretty good marketplace here.