They wrote a ton of top X lists about things that are highly relevant to their audience when top X lists were the thing to do. They have excellent SEO, and bei

They wrote a ton of top X lists about things that are highly relevant to their audience when top X lists were the thing to do. They have excellent SEO, and being an early player and highly linked to gives great Page Rank. They leverage social media quite well (I'd wager a significant amount of traffic comes from SM sites like Reddit/Digg/HN/etc). They produce a lot of content. Their content seems to be edited well, meaning it is well-written, well formatted, and usually not terrible. (I don't particularly care for it, but can see its appeal.) Lots of internal linked to and from related articles and a somewhat well organized site. They allow for readers to comment and they respond to the comments. On top of that, they don't make any fatal mistakes. Their site does not take forever to load. They don't serve too many ads. They aren't on bad terms with any search engines.