I feel a bit silly saying this, but I’ve just now discovered that DT is a brilliant feed reader right out of the box. I had dismissed it because whenever I deleted an article, DT would pull it down again on the next refresh. But if you look at the default RSS settings, DT will delete articles after one day - but only ones that have been marked as read. This means that it’s stupid simple. If I want to keep an article, I lock it, if I don’t want to then I just leave it be. DT will delete it for me in less than 24 hours. How slick is that?
DEVONthink is indeed using a slightly different approach which requires usually little work: Just lock the interesting feeds and/or news and let DEVONthink handle everything else (archiving, tagging and deleting).