I think articles that are not the original source should be merged as comments under the original source since they are often just another news organization or blogger commenting on the source without additional source data.

This will also bring Hacker News more in line with paragraph 5 of the Hacker News Guidelines[1].

I believe even if an article "adds to the conversation" it still isn't worthy of a top level submission. It should be a comment like all the others.

EDIT: To implement this maybe power users above a certain karma threshold can be granted the ability to mark an article as derivative and point to the original source submission. If some magic number of power users do this, the article and the comments are moved and any links to the derivative article are redirected as well.

This will also discourage karma whores and blog-spammers from submitting derivative articles because there is a good chance it will get rolled into someone else's submission that actually submitted the source article.

[1] http://ycombinator.com/newsguidelines.html