Looking at the whole outline of the term's work, it's not immediately obvious that there are changes in the pattern of titling. There are infrequent instances of writers simply not bothering with titles all term -- or at least until mid-November. Instance of titles which merely identify the topic (unnecessary, because the way the postings are arranged makes that clear) seem to become fewer over the course of the term, but it is clear that in the Oleanna discussion, for instance, which runs until the beginning of December, a substantial number of postings are simply titled "Oleanna."
On the other hand, in the discussion of the reading by Rita Joe, Beckys' posting and all those responding to her except Kim's are titled in ways that advertise the point of the posting.
It seems clear that use of titles should be related closely to an awareness of addressivity. I'm not sure I can see this development either, however.