That was a very well-reasoned response, Yahtzee, which is probably the opposite of what many people expected. I think it says a lot that even our most flagrant spokesperson can be mature in his discussion of such a topic.
I agree with you that the "videogames are art" argument is a subjective one that can never be answered objectively, but I don't agree that the question is unimportant. The problem is, that question greatly affects the games industry.
Why can Michaelangelo's "David" stand out in public in all his glory, while "Penthouse" has to be covered up and only sold to adults? Because one is art and the other isn't. It's the same reason some places can have grindhouse films in the cinema, but no blood and gore in their video games -- in the cinema, it's art. If society in general doesn't agree that games /can/ be art, freedom of expression is hampered considerably. Art forms are allowed to bend the rules and buck social norms because they are expressions of art, but if games aren't art, they aren't allowed the same freedoms. You can bet Michael Atkinson would have a much harder time banning games for sexuality and violence if they were recognized as a form of art and not just as toys for children.
It also has implications for the people who develop games. From what I've seen of the industry, those who work in the games industry are viewed as being drones who make toys for children. Because of this, they are compensated accordingly: game programmers make lack-luster wages, work extreme amounts of overtime, and are hired and fired without a second thought. But in the arts, actors, directors, screenwriters -- they all become stars. They are recognized for their work and are paid humongous salaries. Now, this may not be common to all art, but all art forms have their legends whose works are worth millions. Where are the highly-paid artists in the games industry?
Whether or not video games actually are art doesn't matter, but whether or not we view them as art has a significant affect on how the industry and its people are treated. This makes the question, "are video games art?" important for the industry to argue.