Ryan Moran writes: "There is a shift happening in which Google is giving heavy weight towards ACTIVITY on your website, rather than what’s on your site or who links to your site. All these elements are very important, but activity is becoming more and more important.
It makes sense, then, that Google would have started preferring WordPress some time ago, since comments and user activity are easily monitored using that platform.
The folks at Google are really smart, so they are looking at the trends in social media to see how it will ultimately affect SEO. Considering this, it makes sense that they would analyze activity on your site – including comments, Facebook “likes,” and Twitter “re-tweets.” Not only this, but Google is analyzing how long visitors stay on your site, what they do on your website, and if they find what they’re looking for when reading your stuff."