digg recently changes nofollow on externall links

digg is one more of social network with high popularity. Anyone can up to link post in digg and perhaps to can backlink from digg. Now, with some consideration digg developer recently add nofollow to some links on their site, likes snipeds from blog digg that

We’ve added rel=”nofollow” to any external link that we’re not sure we can vouch for. This includes all external links from comments, user profiles and story pages below a certain threshold of popularity(blog digg).

with reason that  changes reduce the incentive to post spammy content (or link spam) to Digg, while still flowing ’search engine juice’ freely to quality content. So new move by Digg is a positive change in my opinion, because Digg decreases the benefit for spammy stories but Digg still helps normal and high-quality stories in the search engines.