When we compute the PostRank scores we do not use global metrics, we only look at the authors past performance. Hence, if Slashdot on average has ~300 comments, a post with 50 comments will get a low PostRank (though we certainly don’t limit ourselves to only looking at the number of comments) Likewise, a blog with an average response of 3 comments will get a high PostRank if he/she receives 10 comments. Of course, you can still interpret PostRank as a ‘popularity’ score, albeit ‘popular’ with respect to the author’s past performance, not the entire crowd.