> Of course we can say "they have retweets" and so on. But those were concepts invented not by Twitter but their users, in the open-source, no-ownership way. Twitter can't claim to say they invented post sharing. They just can't.

Even Twitter's users can't, can they? I'm 99% sure that Tumblr had an equivalent function before people started doing it on Twitter, and I'd be surprised if Tumblr invented it, either.