To tell you the truth, I have never seen a reason to use atom over rss. I have heard allot of people make vague comments on how atom is better, but never any proof or examples. Also, one time I wanted to make a web program that generates feeds. So I went to the rss site and saw a sample document and the spec right there. The I went to the Atom site and couldn't find any simple way to learn how to use it. RSS is better because it is simply, it works, and it can be extended. I don't see any reason for MS to use Atom over RSS.