I don't really see much of an argument against considering video games as art. The longer ones, with stories and what-not are very similar to written books. Both have different methods of engaging the player or reader, but both do provide a fully-fledged story, complete with morals, themes, and a message that can change a player's or reader's opinion on a matter. The shorter games, like in the mentioned Space Invaders controversy, are very similar to paintings. There isn't much of a story to them, but they still are fully capable of affecting a player or viewer.
In general, I'd say that something is art if it's capable of affecting its 'experiencer' in some sort of opinion- or emotially-related way. The fact that 2+2 is 4 isn't art (written on paper, it might be, but not the simple fact itself), while little aliens blowing up the WTC is.