I usually don't say this about people or companies, aware that I am that it's often the other way around. The one saying they don't get it is the one that don't. In this case I am absolutely sure that Google is the one.
They need an API with one call, one that posts a tweet to their service. So people can hook up Twitter clients to Google-Plus, so the hundred million active Twitter users can post to Google-Plus from the comfort of whatever tools they depend on.
Of course it isn't the hundred million that they need, it's the hundred thousand who do all the work on Twitter. The ones that can't be bothered with a service that doesn't have basic rudimentary API support.
Big companies like Google think they're doing us a favor by adding an API. That's because they think not so much like big companies, but like employees who work at big companies. If they really had the ego of a big company they would think like this. You, developer, your job is to make me rich. So get off your ass and write some apps that drive people to my service. Not just any people but the ones who make Twitter sing.
Anyway, when I saw they had an API I was clearing my schedule to hook my tools up to Google-Plus and finally start getting to work making them a success. Instead, I'll get back the work I'm supposed to be doing.
One more comment: They should just support RSS, and forget APIs to read publicly available content. All that's going to happen now is people are going to write apps that produce feeds from their API so they can hook into the reading tools that were written a hundred years ago, like the one Google itself has. What is it about BigCo's that keep them from paying any attention to things they didn't invent? Larry Page: they're wasting your money and your time.