"WordPress automatically notifies popular Update Services that you've updated your blog by sending a XML-RPC ping each time you create or update a post" (in Q2A case it would be all actions from rss feed - create or edit q,a,c),
"Most people use Ping-o-Matic which, with just one "ping" from you, will let many other services know that you've updated. As for why, Ping-O-Matic puts it best:"
"One word: traffic. Blogrolling scripts like blogrolling.com and WordPress check update services to see if you've updated and then shows it on everyone's site -- usually by moving you to the top of people's blogrolling list or putting a recently updated indicator by your link."