Also, "retrospectively making something portable doesn't change it's previous status as a derived work" was if I'm not mistaken SCO's argument for why it should be illegal for customers to run software they'd developed on SCO Unix under Linux. It's not something we should be supporting because it'd a really dangerous tool for locking users into a particular OS. (Fortunately, SCO lost.)
Arguing kernel modules are derived works from the kernel is very very different from arguing user space software is derived from an OS.
That's far from clear. Many core developers (including Torvalds, IIRC, but correct me if I'm wrong) are on the record that they consider Nvidia to violate the spirit and/or the letter of the GPL there. It's just that nobody cares enough to litigate.