I agree with you. Copyright is already automatically applicable. It's not like this further protects anything, it just browbeats the reader. A statement like this at the beginning of an article/talk is a big turnoff for me. Most researchers are excited to share their thoughts and ideas, not interested in jealously guarding them. (Especially when, as here, all the ideas are already known.)
For those saying that Stephen Hawking deserves a free pass, if we apply different standards to different people then that's not morality, it's just convenience. And anyway I doubt it was his idea to post that notice, more likely a misguided publisher.