Forum:Gravekeeper's Servant VS The Legendary Fisherman

Can anyone explain how The Legendary Fisherman is immune to Gravekeeper's Servant? Gravekeeper's Servant required that a card is discarded from the top of the deck. It effects the controller, not the Fisherman. Yet this site and others insist that The Legendary Fisherman, Silent Swordsman LV5, and Horus the Black Flame Dragon LV6 are all immune. I tend to agree with this ruling when I duel, but that's because I'm using the Fisherman. But me and my bro can never come to agreement, and though i hate to admit it, it makes sense that you would still have to discard a card in order to attack. If anyone has an explanation as to why, please reply.