The power of reddit (and for that matter hackernews) is the top-voted comment on most articles is a thorough debunking/rebuttal. I'll often read articles that seem perfectly reasonable but are quickly ripped to shreds by the community. So while you are getting a pre-filtered view of the news, you're not getting a single viewpoint on that news.
Furthermore (edit), the subreddits that you subscribe to radically change the articles you encounter on the homepage.
That's not the case at all IMHO. The top voted comment is just whatever the groupthink agrees is the 'right' stance on that issue.
Over time online communities such as HN and Reddit gravitate towards a specific set of viewpoints.
It means that you start only seeing certain types of article, you only see certain types of comments, comments that 'toe the party line' are upvoted to top, etc.
The other funny thing is how much Redditors etc love to sneer down their noses at the 'idiots' who watch TV. They don't seem to realize that spending hours on reddit looking at funny pictures, being outraged by liberal news etc isn't really any better than watching American Idol and being outraged by the stuff on Fox news.
Furthermore (edit), the subreddits that you subscribe to radically change the articles you encounter on the homepage.