Apple has had some important lessons in pre-announcing products. Remember John Scully pre-hyping the Newton resulting in competitors having plenty of time to steal ideas and reduce the innovation factor while causing Apple's own staff to cut major features to meet the deadline, effectively killing a category changing product. By the time Apple pulled the product together into what it should have been at the start, it was too late. This easily could have been the iPhone.
The Pros and Cons of Secrecy