Assuming you're talking about the Yahoo! News RSS feeds, if you look at Yahoo's terms on their RSS page, they don't require you to post a copyright notice, but they do want you to say "Yahoo! News" or use their logo.
Yahoo! aggregates content, but they license it: they sign licensing agreements and pay AP, Reuters, and all the other providers. So they have a pretty good case for saying that their compilation is subject to copyright (in the same way that a local newspaper can still be copyright even if it includes wire service stories).