Not sure if this an actual response to the OP, but my view is:
1 - Art isn't an accident and first and foremost the question is whether the game, film, book, picture, sculpture, etc. was even intended to be art. Let's be blunt, a whole lot isn't. A lot of material is made simply for entertainment/commerce, be it a Vase to stick in your room from Ikea or a videogame like Super Mario Galaxy.
2 - A lot of people make the annoyingly common mistake of arguing about the whole topic in absolutes - games are Art or no they aren't, or the main goal of films is to entertain. Make a statement like that and you're probably already arguing from a false position. As per 1) it's important to separate the stuff aiming to be art from the stuff that isn't and understand their is a whole range of options
3 - With the rise in impact of games in terms of sales/cultural awareness there's been a perhaps understandable peak in the whole debate in the first place, and to be blunt due to the nature of games a lot of the arguments have been from people with completely uninformed opinions (I'll be blunt here, not all opinions carry the same weight for me based on a whole heap of stuff)
4 - Art that will stand the test of time is, as Rol notes, often nigh impossible to identify initially. Obviously some clear contenders exist, even in their own lifetime, but we'll never know for sure how enduring some art will be (mainly because we'll be pushing up daisies by the time it's classified as enduring art).
5 - Games right now are reactionary and in copying mode for the most part when it comes to many aspects of their content - be it Red Dead Redemption which clearly wouldn't even exist if there wasn't a whole heap of films the developers lovingly (and to be fair I do mean that positively) ripped off or something like copying and advancing a gameplay mechanic. I've yet to play any game that could even remotely claim to have some form of artistic merit without being aware of a heap of superior artistic material in multiple other formats. This isn't a good basis for good art.
So the bottom line for me is clear but perhaps not neat enough for the black/white internet - of course games can be art, probably very few (perhaps none) so far have been, most games are certainly today (and in the past) not created as art but as pure entertainment, and only if we're lucky will we see games that show some indication of being art or even art that has staying power and relevance.
So I do wish the whole topic got a whole lot less coverage, because games claim to being art is weak, that's obvious to anyone who appreciates art across different mediums, and pretty much every game is only made to entertain anyway and has no aspiration to being art in the first place.
Enjoy games for what they are is my view, and don't go trying to talk them up to be what they're not - GTAIV dialogue as good as the Godfather for example - and let's wait until we see some real contenders for art before we even make a big issue about it.
TBH I agree with Ebert's comment about why even argue games as art at this point in time?
Try to be reasonable... its easier than you think...
