So basically company can take your gpld code, extend it, slap their license on the whole thing it and redistiribute binaries without the source code and nobody can slap the gpl back on where it should be because it's a gray area?
The kernel developers and the FSF have always claimed that loadable modules (like the exFat driver) are "derived works", which has a specific meaning in copyright law. In particular, the GPL very clearly says that derived works must be re-licensed under GPL.
The vendors claim that "derived works" doesn't include linked code, or plug-in patterns. They say that they aren't really releasing their own kernel, just releasing the stock kernel with a bunch of proprietary applications on top, along with their proprietary kernel module.
This is not about the GPL'd code people take from you, it's about what they add/change to this code.
Whether you can directly slap the GPL back on these modifications is very discutable. You can most certainly sue them for breaching the license, though.
(and, like sister comment says, this is not what's happening here anyway)
