I specifically mentioned that the reason we don't see any docs, boils down to that the companies don't see enough value in open source development in order to justify the costs involved in being helpful - that includes the cost, in whatever form, of providing documentation, be it in the form of revealed trade secrets and lost competitive advantage, or a patent suit.
Trade secrets are rarely an issue because the market is defined by 6 month product cycles and engineers flow back and forth between companies. Any innovative new idea will either be reverse engineered or patented. Most of the time, it's patented, because patents are cheap and easy to obtain these days. If a feature is patented, the company could freely release documentation and be safe from cloning. However, they still don't release documentation, and the reason why is because _they_ may be infringing any number of an unknown competitor's patents at any given time, and the last thing any company wants to do is invite legal problems. The inevitable outcome of such a battle is cross-licensing, which dilutes the value of the held patents.
The end result is that the best any company will do these days is to provide docs under NDA after a background check. This way, they are protected from secrets being handed over to a competitor indiscriminately, and also from others discovering that their patents are being violated. Unfortunately, for some companies, the risk is too great compared to the benefit to even justify an NDA policy. This stance is the most common in the industry today, and is the natural result of a system where frivolous litigation is the norm and where the PTO grants patents willy-nilly to anyone who asks.