The idea is that in one social networking newsfeed, say in Google Buzz, you would see not only the activity from your social network in Google Buzz but also the activity from your social network in Facebook or Chatter.com or LinkedIn.
The goal is to create a mixed newsfeed that would show what is happening on Google Buzz, Twitter, Facebook, LinkedIn, and any other social network that supports the standard.
Google is criticized because services like GoogleNews provide the sorts of stories that in another era you needed to feed change into a newspaper vending machine to get.