IRT the realism of graphics vice the mechanics of gameplay... If you RTFA, it solely concerns itself with graphics because gameplay has been perfected, as if these are the two major factors in a game... I disagree. The story and the stylistic choices are two major contributing factors that make this argument irrelevant...
Realistic graphics are just a tool. Realism is by no means required, but realism can make introducing the surreal that much more impacting.
Take the horror FPS genre... You use realistic and gritty scenes to set the tone... You slowly (or abruptly) twist it on its ear with small surreal aspects (ghosts, shadows rushing by, strange noises) to make people feel uneasy, and then start an assault. Good gaming with a high (although not perfect) level of realism results. But because the world and storyline dictate some unreal occurrence, this is forgivable. If your ghost is a flickering translucent spectre, then it adds to the realism. If it looks like a ghost from Pacman, or a guy with a sheet over his head, well, you've ruined the game with surrealism...
Or in war FPS games... Realism lends a certain credibility to the chosen mechanics of game play. If you want to relive storming the beaches of Normandy in WW2, then semi-accurate maps along with realistic looking environments, period and situation accurate decor and dress, and accurate weapons and vehicles, are what is going to make that experience fun.
On the other hand, if you want to relive storming the beaches of Normandy, and you do it in a cell-shaded world, then it doesn't FEEL like storming the beaches of Normandy... I'd expect (and want) it to be more "arcade"-style game play. Likewise, if you throw in railguns, jetpacks and other things that weren't part of WW2, it wouldn't be as fulfilling an experience for a game set in World War 2. (And before I get flamed, Wolfenstein was never intended to simulate WW2, and never really had much realism to begin with).
Basically, if your game's level of realism is consistent with game play, story, and style, then realism is perfectly justifiable.