I agree with you, but if I had to choose between a functional Linux driver and documentation, even as someone running BSD, I would take the Linux driver every time. A functional driver with source lends some confidence that nothing is missing. Documentation can be well-intentioned, but it is rarely so complete that you could write a major piece of software with nothing else.

Of course, drivers+documentation would be even better :)

I'm not a driver author, but I'd hazard a guess that the source for a Linux driver is a lot easier to port to BSD than the binary.