I have seen a similar question on http://stackoverflow.com a few days ago .
I think my answer may not help you .But There are some other examples mentioned which were built like digg already on wordpress platform .
http://nestdev.com is the best one I have ever saw .
(Sorry If My answer doesn’t fit to the question .I didn’t find comment option here for this question.May be my reputation level is not enough to use the option to comment.SO I have post this as answer)