http://www.copyright.gov/circs/circ1.html
TRANSFER OF COPYRIGHT
A copyright may also be conveyed by operation of law and may be bequeathed by will or pass as personal property by the applicable laws of intestate succession.
It looks like their true beef is with the laws of intestate succession---which generally don't recognize the fraudulent theory of "gay marriage."
This has been a problem for as long as 80 year old men with weak hearts have been marrying their 20 year old secretaries and willing everything to the young widow.
Doesn't mean it isn't challengable in a court of law and that heterosexual spouses, children or grandchildren won't be able to get their greedy little hands on copyrights you left to someone *else* who you found more worthy.