I here people say that PR is improved by gaining more valuable external backlinks to the page in question. However wouldn't this mean that all or most of the DP topic pages have a PR of 0 because nobody backlinks to a specific topic page?
Check the old threads, quite a few of them have PR. In any case the linking structure of vbulletin isn't that good in properly distributing PR to each and every thread of such a large forum.