I believe that the sort by "Recent" filter on the Community Home page only shows the most recent Discussions posted.
It is possible to implement a sort that filters by the most recent dated comments to any discussion.
You have this option when when you select a search TAG. It then gives you the options to sort by Relevance, Date or Comment.
it would make general browsing more interesting any throw previous discussions back into the limelight for further input or help?