If all we should care about is the story, then how come we're all not still playing Eye of the Beholder, or better yet, pen and paper AD&D? I mean, if graphics are nothing in the grand scheme of RPGs, why are companies like, say, Bioware or Bethesda (albeit that's a stretch) even bothering?
Because graphics mean everything for sales. When you first see a game, it will probably be a screenshot on the web, in a mag or on the gamebox itself. To see a game with gorgeous graphics gives you a good first impression, and draws your attention to the game. And more attention means more publicity, which stands equal to good sales.
Let's face it. Good graphics is why most people buy a game, but it's
gameplay that makes them enjoy it, and play it for a long time.