Bad example, but I'll do it anyway...
These are some of the pieces I found:
http://www.gamespot.com/pc/rpg/neverwinter...ex.html?page=29
Considering how NWN turned out and what those pieces try to convey; I see your point. But look at the concept art of BG for example: areas, models, gear, storyboard; you can see what the general feel of and sights of the game might be. As not a whole lot of NWN concept art where given to public and therefore you can't really make a call for it's relevancy. But that doesn't really matter; when I see concept art, and I mean real art; not sketches of models; I either get a fix of of the feel of the game, an estimation how the atmoshphere might play out to be; or if the art is really bad it leaves me with foreboding "This is the stuff they're gonna base a game on? oh, shucks...-feel. To me; art is relevant, but only before the game is out, after that it becomes useless eye candy.