In general, people working for Apple believe in the reasons for the secrecy. It's easy to motivate people to keep their mouths shut if they understand the need. When leaks happened, even simple things like leaked copies of Steve Jobs' or Tim Cook's company-wide e-mails, we actually felt angry that “one of their own” would have betrayed our trust.

Additionally, the feeling of fear that most outsiders assume that Apple employees feel isn't really there. As long as you don't try to cover your ass, by not reporting leaks or losses you were involved in, you'll generally come out OK. Even in a famous, well-publicized lost device case, not much happened to the person who lost the device. This is because they followed proper procedure, and reported the loss as soon as it was discovered.

There was one occasion where I thought I had lost prototype devices, and it was well before I had any experience in dealing with lost devices, so I was a bit anxious. The instant I realized that I didn't know where the device was, I sent an e-mail to my manager, sent an e-mail to Apple security, and marked the device as "lost" in the records. I got a phone call from security and explained the situation (i.e. when/where I had last seen the device, the device's serial number, etc.). The device was found a couple of days later (it was in a filing cabinet in the office of a coworker who I had lent it to as a test device, but hadn't marked it as transferred in the tracking system). I asked my contact in security what the consequences for me would be, and he basically said that I had followed procedure, and that there would likely be no consequences (and there weren't any).

Another occasion, while at WWDC, I called something by it's working name. This was a product that we had all known by a particular name for years, and just weeks before announcement, the name was changed. The reaction to that was simply, "whoops, mistakes happen." They knew that no malice or incompetence were involved, and there simply wasn't an issue.

Basically, my point is, the security and secrecy at Apple isn't maintained through fear and control, it's maintained by making the employees feel that they have a stake in the company, and by treating them like competent adults.