facebook does not allow google to mine 'likes'... if that data is coming from Twitter - Google does not have access to it.
And hence we see the strong movement at Google to roll their own, Google+, and make it successful. They need to get the flavor and the detail of the real social networks that move buzz and communication.
For example, if they can see a REAL buzz developing about something very new, that would be a more helpful signal than traditional "freshness". Right now, conventional freshness can often promote a site beyond all reason, and that opens a loophole for spam.
The actual social networks themselves are just what they are - a feature of the human landscape and culture. These influence connections will be significantly the same, no matter where or how they interface with the web. Over coming years, we'll probably learn more and more how that works.