I'm certain that if alive and working today, he'd know you can't have a press event and try to embargo the information.
In recent days both J.K. Rowling and Nokia have bungled such situations. Rowling was announcing the new Pottermore web site. Nokia was giving a preview of a forthcoming product.
As this article points out, Apple, among others, knows that you release the information when you're ready to have it released and you really leverage the immediacy. I disagree with the premise of the headline -- it's not only tech product launches the new principles of p.r. apply to. As the internet has become a key source of fast-breaking information, the rules apply to all news
Below is the Twitter feed of BBC's technology correspondent at the Pottermore presser, and here is his later blog post on the subject.