I noted a [deleted] post at the bottom of this thread, where the replies indicate that "Twitter couldn't have known about G+", hence I guess the [deleted] post had similar sentiments to me. Google having social aspirations has been well-known for a long time. I could very much imagine Twitter writing a contract which says that the stream was only available to Google for as long as Google wasn't directly competing with Twitter. Google couldn't sign such a contract. Google+ is direct Twitter competition.