The reasons include delicious' greater flexibility, configurability, wider user base, and (important) the existence of an API. Delicious is owned these days by Yahoo!, while Newsvine is part the new-media extension of old-media behemoths NBC and the Washington Post.
I've revived the old scrapbook concept that I was using a few years ago, however I've outsourced it to newsvine.com.
I'm using it to link to business and politics-related items about the Cricket World Cup - I figure there will be enough bloggage and reportage of the match play that I can stick to my own niche.
Occasionally there'll be a story which I might want to blog further over here, but for all the clippings, please go to rickeyre.newsvine.com.