I think part of this is the 'frontpage echo effect'. Quite regularly there'll be a few days/weeks of articles about either a particular topic (that is not time-

I think part of this is the 'frontpage echo effect'. Quite regularly there'll be a few days/weeks of articles about either a particular topic (that is not time-sensitive), a particular theme, or from a particular source. Sometimes it's submissions of interesting links from the discussion of a previous article (I've done that more than once), sometimes it's from people who decide to read past entries from the same source (or add said source to their reading habits). And I'm sure there's other reasons why this happens.