There was one guy who was strung up as a leaker ten years ago. Don't remember his name, but it was a big deal.
AMD's culture is just different than Apple's. For one, there are no "secret teams" like iPhone, iTablet, etc. (well, at least none that I knew about). For another, developers have real autonomy to make business decisions, something that would never happen at Apple. For instance, I, a lowly intern, redeployed software to the production line during an emergency. If something went wrong, chips would actually stop rolling out of the factory. I would imagine normal (non-senior) Apple engineers don't have that kind of autonomy.
The other major difference, which perhaps you caught above, is that AMD actually manufactures their own stuff. So, not only are there US engineers, but engineers overseas in the plants that AMD owns, engineers in Dresden, etc. Not to say that foreign engineers are somehow bad, but it is a lot harder to control leaks when you have engineers working literally 24/7 all around the world. And at the scale that you're making your own stuff, there are just more people than there are at Apple, and things are way harder to control. It's like herding cats.