Copyright law works, to my knowledge, the same way. If you don't defend your ownership of the copyright, then you risk losing.

And there are owners of "significant" applications who are more than happy to press the issue, given the opportunity. As has been mentioned before, "bash" wouuld be a good example, and Stallman and the FSF would probably happily go for the carotid artery if they saw someone violating the GPL on it.

D