No offense, but what makes you think that Google and Facebook 'imitated' Diaspora? It's a naturally occuring idea that is visible in real-life interactions. Circles seems to be a lot more intuitive and user-friendly than what you guys 'invented'.
AFAIK someone who worked at google researched heavily in the topic of circles. He ended up in facebook. I don't think Google imitated Diaspora as they had given this circles phenomenon adequate research and breakthrough.