I've been familiar with Digg for a few years now, starting around early 2008. And the truth is, though Levinson has a good theory about how Ron Paul's popularity on the site may have been skewed because of the 13-17 year old age group, I think he overlooks many things regarding how articles and topics become and remain popular.
Though I haven't used the site in months, whenever I did, I would merely scan the front page and possibly search a little more if I felt like it, but would generally only be interested on what were the top articles of the day.
And at least for me, I believe that that's how the majority of Digg users use the site as well. Unless you're a Digg and web junkie, we never really go out of our way to find articles that we like, but just like seeing what's trending and is relevant at the moment on the front page.
Because of this, the election, and other political articles were definitely going to succeed. Even if you're not overly political or an extreme activist, you'd at least be somewhat interested in the articles on Digg during the primaries and the rest of the election, because it's the news that was currently relevant.
Most other times, I can remember, there were many posts about technology and really random stories that became popular. If it was funny, cool, or entertaining, it made the front page. And if it had a good title to convince people to digg it, people, including myself, would do so even without actually reading the article.
I think it's important for everyone to know that most Digg users aren't extreme, but are just merely curious about what everyone is digging, and will jump on the bandwagon most times.