If you post a reply, then immediatley look at the list of replies, your reply will of course be listed at the top at that moment. Hence, "Bump to the Top", "BTTT," or "Bump"--signifying that the reply is for purposes of attracting attention to the thread, more than or to the exclusion of any substantive comment.
John Rob is announcing a way to call a thread to the attention of a pre-defined group of screen names of people whom the bumping individual hopes will be interested.
A "bump_list" is like an "imaginary FReeper" whose interests I would like to follow.
There is no need for a "lowbridge_list" because there is already a REAL (sort of) lowbridge that I can "follow around" by searching for Articles + Replies addressed to:lowbridge - that SOMEONE thought he should see, like THIS reply. ;)
Now, you can "follow around" the posts addressed to:bang_list etc., as well.