There's an interesting discussion about the whole topic on the Phoronix forums about this. Some people claim that removing them and Nvidia's current behavior is a DMCA violation:

1. The kernel includes IP only licensed under GPLv2.
2. While a module linked against the kernel isn't necessarily a derived work which in turn would need to be licensed GPLv2 as well, there are specific interfaces that are meant for internal use and by their very nature would make your work derived if using them. These are the interfaces marked EXPORT_GPL_ONLY.
3. Using these interfaces with a module not licensed GPLv2, you taint the kernel and violate the licensing.
4. Removing the check, you aren't necessarily yet violating GPLv2, but you're removing a technical protection measure which is a violation of the DMCA.

It also raises the question why you'd remove checks that only prevent a possible GPLv2 violation if you're not violating GPLv2 anyways as Nvidia claims.