These days, many sites, from the New York Times to BusinessWeek, have a Digg button for their stories. But suppose you are a new user to Digg; think about what actually happens to a story when you submit it to Digg. It goes straight to the first page in the Upcoming section, along with thousands of other stories per day. Because so many other people are submitting stories all the time, newly submitted stories quickly get pushed out of the first page and towards oblivion.
This points to one of reasons why so few Digg users control so much of the content: their network of Digg friends. Your Digg friends can see and follow which stories you've dugg, and more importantly, which stories you've submitted. In fact, many Digg users use their friends' profiles or submissions page as a way of guiding them to interesting upcoming content. Making friends on Digg, and having people befriend you back, is crucial to helping you digg stories that they submit and vice versa.