That is incorrect. No federal court case has invalidated a state law limiting marriage to heterosexuals. The law struck down in Nebraska which included marriage, was struck down for the remainder of the law prohibiting unspecified associations and as such violated the 1st and 14th Amendments of the Constitution. Every federal judge has recognized that a state has a compelling interests in promoting procreation, and therefore may discriminate in the area of "marriage".
So far, perhaps, but frankly I don't like the possibility of this landing in the realm of some liberal judicial loose cannon.