>>pg+p2
Systematic factors inherent to social news sites degrade their quality over time. Voting is broken because of the nature of the people who vote the most and thus have the most influence on the front page: They are people with too much time on their hands. That is, anyone with a worthwhile opinion is off doing other things more important than commenting or voting on a news site.
This isn't to say I agree, I'm just trying to summarize the relevant bits as best as I can.