Linux is not in the public domain. Linux is a cancer that attaches itself in an intellectual property sense to everything it touches. That's the way that the license works.
Bio: Russell Dana "Russ" Feingold is a lawyer and politician from the U.S. state of Wisconsin. He is a candidate for the U.S. Senate in 2016, and previously served as a Democratic member of the U.S. Senate from January 3, 1993 to January 3, 2011.