I find this argument to be humorous: as a Kings fan, I've argued with several Lakers fans for the past five years, who try to claim that Lakers/Kings (which could be argued is essentially like the Yankees/Red Sox rivalry, although on a much lesser scale), isn't a true rivalry simply because the Kings have never beaten the Lakers, and now I've seen Anglesault claim that Yankees/Red Sox was only a rivalry simply because the Red Sox had never beaten the Yankees...
Just goes to show that, if you spend enough time on the internet, eventually you'll hear everything...