I think you (and many other people here) are confused about what Social API really is.
It's like BrowserID - a protocol that enables authentication. Facebook can implement BrowserID, StackExchange can implement BrowserID, Google can implement BrowserID; you get the idea.
The same goes for Social API. It's just a protocol for social networks. Anybody who wants to create a social site, can support the Social API and users can enable it to work on any site that offers such functionality.
It's like BrowserID - a protocol that enables authentication. Facebook can implement BrowserID, StackExchange can implement BrowserID, Google can implement BrowserID; you get the idea.
The same goes for Social API. It's just a protocol for social networks. Anybody who wants to create a social site, can support the Social API and users can enable it to work on any site that offers such functionality.
Social API IS NOT "Facebook in my browser".