Overall, when determining whether a piece of work is art or not, it comes down to the medium. I consider comedy to be art, but you wouldn't judge George Carlin by the same standard that you'd judge Beethoven by. Games can be art, but they have to know their limits.
Game designers are, for the most part, not writers. That's why so much storytelling in games comes off as forced or cliche: the developers just aren't writers. Even in games where the writing contributes to the atmosphere, the writing itself is usually minimal. Half-Life 2 is an excellent example: just enough characterization to give each character a distinct personality without distracting from the core gameplay, which is the meat of the issue. I haven't played very many games recently, but I hear that titles like Bioshock have a lot of value in their writing. That may be true; I'll believe it when I see it.
The people who make games are called "game designers" for a reason: their profession is to design games, and when it comes down to it, the principles that guide video games are the same principles that guide every other type of game. A good game uses these principles to deliver a fresh and fun experience, with attention to presentation.
For large values of one, one equals two, for small values of two.