This article is very enlightening as to why Gamers are losing the argument over games being Art.
Ebert's whole point about games NOT being art is that by their very nature they're interactive. See http://rogerebert.suntimes.com/apps/pbcs.dll/article?AID=/20070721/COMMENTARY/70721001
"How do I know this? How many games have I played? I know it by the definition of the vast majority of games...player control of the outcome. I don't think these attributes have much to do with art; they have more in common with sports."
His point is this: the player influences the outcome of the game, therefore the game can never be an accurate expression of the artist's (Game designer's) vision. Without that expression, there's no meaning to the game, and hence no art.
Some will argue games that are story driven, such as the Final Fantasy series, can artifically limit choice to a series of progressions that ultimately tell the same tale. However, no two games will ever be the same, and thus the designer's vision will ultimately always fall short and thus the nuance of the craft are lost.
Gamers want to redefine art in the method of Andy Warhol -- anything can be art. But that's never going to fly, or else we must redefine EVERYTHING as art, utilitarian or not. Ebert himself, has perhaps unintentionally given us the direction that this argument must flow towards.
What gamers fail to realize is that for Games to be considered art, we have to change the definition of what a GAME is. If designers and players alike only realize that games at their core are 2nd Person Narratives, we can better frame this argument as a style we can defend. The aesthetics of the game, the mood and feel, are only details, not the art itself. The art is in the expression, the performance.
Unlike sports, where there is a set of rules players have to follow, video games are about the experience the player has while playing within the bounds of those rules. The RULES ARE NOT THE GAME. The emergent gameplay (http://en.wikipedia.org/wiki/Emergent_gameplay) is what makes the game art. It's the player's creativity in response to the game design that makes a game art.
I challenge you that games are NOT sport. They are the tools by which the Performers (which we call players) express themselves through improvisation within the bounds defined by the Directors and Producers. We are all artists, our controllers are our paint, our consoles the canvas, the Television the gallery. And through the internet, the world becomes our audience.