Actually, it's annoying to get 5 URLs pointing to different articles about the same thing in the RSS feed - if I'm interested in reading the discussion about an event, I can open up the comments for a single URL and find other interesting URLs in there.
It also means that comments about an event don't get fragmented into multiple threads.
The only reason I can see to post in separate threads is to gather karma, which is a shame as it doesn't benefit the site as a whole.