Author here. You may also want to check out a more recent post I wrote about blogging that focuses on those "side benefits": http://nathanmarz.com/blog/break-into-silicon-valley-with-a-...
I prefer to leave blog threads open since I don't know when people will find my sites and contribute. Except for posts really connected to a specific event, technical posts has a larger life.
I dislike closed comments though sometimes I have to remind people to look at the date of the post :-p