If he isn’t even bothering to experience games or to do even a smidgen of research before starting a critique, can we really trust that he bothers to do due diligence in his film critiques?
Well, I personally don't think that his post(s) about games have any bearing at all on his merits as a film critic. The guy just doesn't like games, or at least he's stuck on his definition of what they are and isn't particularly interested in changing it.

He has lapsed into condescending jerk mode a few times, especially on twitter, but again, I think he's partly entitled. I haven't even bothered to read the comments on his post, and he's been getting deluged with them. I know when I spend more than a few minutes reading a forum filled with nothing but videogame players, I get the urge to start punching and stabbing, and I'm ostensibly on their side. Maybe if these discussions keep popping up, the audience (myself included) will eventually calm down and grow up a little.

Who’s to say a beautifully made car isn’t art?
I think I am, because it's not for the purposes of what I'm interested in talking about. I think a big part of the reason the games-as-art topic gets so tiresome so quickly is because it always gets derailed into navel-gazing "what IS art?" pontification, which just doesn't interest me at all.

The layman's definition of "art" that I'm interested in: exists for its own sake, communication between artist(s) and audience, intended to convey some meaning or idea in a manner unique to its medium. So a car wouldn't fit that narrow definition, because it doesn't "mean" anything.

I’m guessing that many of the people in the video game industry got in for the same reason. They didn’t do it because they wanted to become rich and famous, they did it for love of the medium. They did it because they want to make great games.
Of course, the business side of things isn’t interested in that; they’re interested in selling product. Just like the film industry. Michael Bay doesn’t get millions of dollars to make films because the producers think his work is art, and the producers of the AAA games probably look at their product the same way. All they’re interested in is selling units. Again, they are entertainment INDUSTRIES. I’d say the biggest difference between the game industry and the others, though, is they haven’t realized that art sells.
Of course there's always a tension between "art for art's sake" and commercial art, there is in any industry where "creative types" are involved, and there always has been. People gotta eat.

But it's not so clear-cut: artists want to make great things, patrons and business types just want to make money. There are publishers who want to make great movies/games, and there are filmmakers and game developers who just want to make money. To use your example: I've never seen or read an interview with Michael Bay, but it wouldn't surprise me to hear that he got into the business out of a genuine desire to make great movies, and he believes that he really is making great movies that happen to be profitable. And the converse of that: I'd say that the Coen Brothers are the greatest filmmakers alive today, but they've still got to keep an eye on which movies are going to sell (No Country for Old Men) and which are their own personal projects (A Serious Man).

My point is that, as Ebert points out in his post, "motivation" only goes so far, it's not a given, and wanting to make art doesn't guarantee that you'll make it.

Where I think games are different, and the reason I think the question "Why do I care if someone says they're not art?" is important, is because that motivation is nowhere near as black-and-white as it is in other media. You say that a lot of game developers got into the business because they wanted to make games; I ask whether they got into the business because they wanted to make art.

You could be a game developer and make a valid case that a "great game" has nothing to do with art, using my definition of art as conveying "meaning." You could say that the best games are abstracted, like chess, and it's not their place to convey meaning, and still make great games. You could say that games are like sports, and make fantastic sports games.

And, you can make the claim that the developer's voice isn't important, that games are all about enabling the player. (Which was basically Ebert's initial argument way back when). That's not "art" by my definition, because the sense of communication has been lost. But it's still a valid way to look at games, because the player's interaction is what differentiates interactive media from traditional media.

There are plenty of people who are saying "of course games are art!" and then defending it with claims like "they've got lots of artists working on them" or "they've got lots of art in them, so they must be." That doesn't make the game itself art, though, and that's the part that I think is worth arguing for.