Google Circle Social Networking site from Google

The big rumour out of the big SXSW shindig this weekend is the imminent launch of the new Google social media network, Google Circles. The question I have is, why? It's not like everyone is sitting around saying if only we had another social media network we could all join and jump on that bandwagon. I understand that Google is deeply concerned about the fact that the social media networks are going their own thing without it. But the question here is are they serious about creating a new social media network or is it a pressure tactic and leverage in their potential purchase of Twitter? When I read these articles and commentary about Google Circles, I always think back to Google Wave - wasn't that supposed to be Google's big entry into the social media space? So I'm looking at this with a degree of scepticism and wondering if it is true, and if it is, I don't see an enormous rush of people moving from Facebook and Twitter to Google Circles.