Not only that... once they violate the terms, they have lost the right to distribute the work, forever. It doesn't matter if they start complying; if they ever want to ship again they have to get a new license from the copyright holders, e.g. Harald. Technically, anybody who has code in the core kernel, or in the drivers they use, can make them stop shipping, any time, for any reason, or for no reason. Lacking approval, the violators may be able to sell their assets to somebody else (or back to themselves, under a different corporate shell) and start over.
Given the curmudgeonliness of some kernel coders, it's remarkable that this doesn't happen frequently. I attribute that to curmudgeonly coders' distaste for the courts exceeding their annoyance at software freeloaders.