Neither Samsung nor Apple is a single entity. Samsung has it's own set of profit overheads for memory vs. tablet. The guys supplying the components to Apple need Apple no matter how much the tablet team would like to cut them off at the knees.
Apple cannot pull 100% volume out of samsung. For nand flash, samsung has 40% market share. Only they can do is to reduce the volume, while other customer will be happy to use samsung chip. samsung SSD is in fact a factor for product choice, so samsung has nothing to lose in this game.
Truth behind the scene is.. Apple was ordering at a price lower than the manufacturing cost. Samsung said NO WAY! SK Hynix and Toshiba said NO WAY OUT! other than Apple. These two underdogs accepted Apple's offer very unwillingly. Still complaining..
Unfortunately there are no other customers that can provide Apple's volumes. And remaining ones might have supplier agreements with other manufacturers. Ineffect, there is not much hope of "diversifying" and keeping the volumes(without which even the price might go up!)