While I'd not be surprised to see corporate security better than the FBI's stuff[1], I find it hard to believe you can't just get agents on the inside for the amount of money involved. So secrecy seems so unlikely to be useful against the companies that can really benefit from that knowledge.
It reminds me of Nikon not documenting their white balance settings in their RAW format. Just stupidity all around.
1: A long time ago, I saw Microsoft Internal Affairs in action. They were fast and setup a sting, complete with their own undercover agents/turned insiders, in a matter of weeks from first tip-off. I'd imagine companies like pharma or chips, would have even more severe response. Whereas in the FBI, one multi-decade mole was actually caught once or twice, but talked his way out. At one point, he even led the investigation against himself.
Here's another, Microsoft Internal Affairs more recently in action:
http://www.nytimes.com/2014/03/21/technology/microsofts-soft...
While the knockoff market is very real, it always seemed far-fetched that NDAing data sheets would be that much of a protection. You would think a sophisticated shop has enough relationships to get the sheets via a close contact, friendly supplier, etc..
IMHO NXPs datasheets were usually ok (for common parts, of course)
Which is funny because at one point I stumbled upon a web site that was selling layer-by-layer microphotographs of the chip I was using. They weren't much use to me, but for someone wanting to reverse engineer the chip I'm sure they would be a lot more useful than a complete description of the chip's external interface.
[1]: http://uk.farnell.com/nxp/mf3mod4101da4-05-1/rfid-read-write...
Yay security by obscurity.