What do you think is worse? People making new threads for a Pagerank update or people posting in the thread "nothing here yet" "its not an update". Personally I think people replying to the threads is more annoying than the thread being started in the first place.
Both are annoying, but if people didn't respond with the usual "not here", "show proof", "no update for me" one liners then the threads wouldn't be so annoying as they will just die off and sink off the page.
If people will not start all those repeated pagerank threds, no body is going to post. So simple. People need thread to post useless and PR threads are good for this.
Making PR update threads is not annoying, you must consider that it is still part of Google and SEO...that's why i both for the second one!
Some people are just new - so that is the main reason for having stupid threads... I would make a separate category of threads. Look like we are getting a PR update every other day...