Not sure if I am understanding fully, but all Threads are usually floated to the top of any Section's list, according to the last time they were posted to. The most active Threads will always be at the top, and the Thread with the most current Post will be at the top.
Not sure if I am telling you something you don't already know, but I hope this helps. If it is not what you were looking for, perhaps you can elaborate a little.
Unfortunately, from my understanding the "recent topics" section has been eliminated from the PlayStation.com message boards. There are spaces that mimic this functionality, like at the bottom of the "Games" page, but for the site's entirety it seems we're no longer outfitted with all posts centralized into a single container.