Clearly such a breakdown would be interesting. But in context you seem to be implying that a video call "doesn't count" as a Google+ usage. If you, say, take a Instagram photo or message someone using Facebook chat but don't look at the front page, are you "not using Facebook?". I'd expect Facebook would count you as a "user" for the day, no?
I'm not saying 100,000 is an unfair statistic, but what I meant to get at instead was growth through g+ versus inclusion through tack-on services (a totally valid and excellent way to bring users into your product :-) as I tend to agree with some of the other comments describing it as "the path of least resistance" for sharing content through google.