All kinds of projects at Apple have their own disclosure forms, and you are only given one to sign if it's deemed necessary to your work. My responsibilities on this project didn't entitle me to be disclosed on it, which led to all manner of hilariously frustrating guessing games as I tried to deliver on the requirements without actually being told what they were. Conversations regularly went like this: "I can't tell you that that approach won't satisfy the requirements, but I would think twice if I were you." Ultimately I think that I puzzled out what was needed and successfully delivered it, but the method was pure madness.
This wasn't even some new silver gadget launch, it was an infrastructure component to a future product launch down the road. Yet everything and anything can be given the top secret treatment.
Why is that? Running a disclosure-required project is prestigious. Being disclosed on projects is a badge of honor, almost even a high score board, and not being disclosed is used as a weapon in big or small ways.
Anything that Apple manages to ship (in my experience) is in spite of their corporate culture, not because of it.