I've seen various reasons for NDA's and some good solutions too.
1. "Corporate Policy". This seems to translate as I don't know but it
would be easier to skin elephants with a toothpick than change it. These
people seem however to understand commercial advantage
2. "Support". This happened with Connetix and the quickcam. They didnt
want to get millions of weirdo's phoning up saying "I've plugged my quickcam
into my gameboy using the board I found in the magazine" and it doesnt work..
You can now get documentation that requires you promise to specifically
state that the code isnt not theirs, not supported by them etc.
3. "We never thought about it". To an extent this happend with localtalk
boards. Most of the info is now on the net in the form of DOS driver source
once people asked enough.
4. "Very clever hardware". This I take with a pinch of salt. I've
reversed a couple of boards the legal way (looking at the chips etc) and
to be quite honest its not always that true. Sometimes it can be.
It's up to the vendor I guess - the sad thing is they lose the ability to
make easy drivers (by letting someone write it for them for Linux), and users
lose out through less support. I have had one fun conversation. Someone was
ranting about how DOSemu let people monitor ports and watch I/O access and
it was terribly wrong and evil. He was even less impressed when I pointed
out that its not hard to do directly on the bus, by linking a test tool with
a loadable module (remember its only a .o file) and other things ;)
Alan