The comparison I always fall back on: In one of my university creative writing classes, one of the students asked our professor, "What separates me writing completely random words from cubism?" My professor's answer was "Well, you aren't Gertrude Stein?" More than anything else, being art means being accepted by the greater artistic community. And yes, it's pretentious.

One aspect games lack in being deemed art is the intent and artistic expertise of their creators. Few games are created with the intent of creating art. Fewer still by the hand of a lone artist or orchestrator whose vision they enable, let alone some mutual collective of artists. Rather games are an exercise in engineering that, when they do feature artwork, generally do so through incorporation as composition, not through becoming art in themselves. The author of the Gamespot article touches on this in referring to "translation."

There's also no concrete line to cross. As with Gertrude Stein and cubism, some writing is deemed art, and some isn't, and often the difference is something trivial and unquantifiable. The same applies to music, movies, paintings, etc. Then take it a step further: Is advertising inherently an artistic? Sports? The news? You'll find that those devoting a significant portion of their life to them tend to be the most inclined to view them as art regardless of what the greater artistic community would claim... which is the problem with gamers, myself included, discussing whether games are an artform.

Mind, mainstream has nothing to do with it: Games are mainstream, and often it's becoming mainstream that undercuts consideration as art.