Everything. Every time Nvidia does anything with Linux they are huge dicks.
Everything from their SATA devices, NIC device, graphic devices, ARM systems... they try to pull the same bogative crap that they pull every time they introduce new products. Sometimes like with the nvnet versus forcedeth they will drop the closed source driver after the reverse engineered one opens up, but that's only after people spent lots of time and effort.
The keys are the drivers, and they are given to you. Also, you know in advance that you will not get specs.
Car companies also do not disclose the proprietary technologies they develop for their cars. The car you drive has closed, proprietary tech in it. You still drive it, don't you? Your own argument works against you, because you have a very wrong idea about what your rights are. You have the right to *request* specs, but they have the right to deny that request.
Also, don't forget that unlike car manufacturers, NVidia does not actively hinder other people from manufacturing custom keys (Nouveau).
In the US, at least, there are laws that the car manufacturers have to allow 3rd party mechanics the ability to work on their cars. They can't force consumers to get work done only in their own shops (by restricting info on how they work).