The experiment was whether the abstract power of his talent, and of the music he was performing, would cut through the fog of people's commutes. The unstated assumption is that if it doesn't, there's soemthing wrong with us.
The WaPo article deserves some criticism, but not for the questions it's asking. As such the piece is a really incisive look into high-cultural values that most of us are not comfortable questioning so explicitly, and Gene Weingarten deserves kudos for having the cajones for approaching Joshua Bell with the idea. As does Bell, who followed through on the experiment and seemed very forthcoming about his subjective experience. Indeed that may be the most interesting part of the piece. The rest is entirely predictable.
The problem with the article is the unstated assumptions buried in this experiment, and the often moralistic tone employed in discussing the whole enterprise and its outcome. Weingarten beats the reader over the head with said assumptions roughly enough that it seems he was intentionally trying to get us to notice them - but if that was really the point of his whole experiment, he doesn't ever allow that he realizes this. Some of them are:
Assumption #1: Beauty in art is context-free. The experience of beauty should radiate through and wake us up, regardless of our background. Kandinsky is often held up as an example of someone whose art showed his belief in context independence, and consequently as the classic example of the failure of modern art, precisely because it could not be reduced and purified to its essence. The National Gallery Curator in the article understood this clearly and was unusually frank about it; Joshua Bell did not. What's most interesting about believing artistic beauty is so strongly objective and context-free is that this would also mean it would be easy to build a machine to measure beauty, which (I would wager) most people who think art is context free would not want to believe.
Wassily Kandinsky, Yellow Red Blue
Assumption #2, related to the first one: Beauty in art exists on a one-dimensional spectrum. Should these people in the transit station have reacted the same way to someone playing Slayer, or Elvis, or to the world's best mime? If not, why not? The obvious answer is the presumption that classical music is better.
Even leaving aside debates about the virtue of one over another set of esthetic values (i.e. metal vs. classical, of course) I do not have adequate ability even as a music appreciator to hear why Bell is so much better than anyone else. (I do however claim such abilities where metal is concerned, and exercise them frequently on this very blog, of course for your benefit dear reader.) Again, this a) assumes the existence of only one dimension along which skill can be appreciated, but also b) requires special effort from appreciators, which wouldn't be so bad if c) there wasn't a moral judgment and presumptuousness that so few people have this skill.
Assumption #3: There is a moral failure in modern life if it does not lead us to appreciate artistic beauty - when and where the artists want us to. The fact is that we're saturated with media today, and we hear far more music and see far more art than people did even fifty years ago. (Indeed, American Gen X and Yers are more likely to listen to classical music than our parents.) Notice that it was the children in this story who stopped and listened to the violinist, because it was probably the first time they'd heard a violin. If we lived in medieval Europe when most people rarely heard music, they would have stopped too, not because medieval peasants could appreciate artistic beauty better or their lives were somehow more in balance, but out of sheer novelty, just like the children did.
But more important here is the sheer presumptuousness of such an attitude on the time of the passersby. I say this is good art, and if you don't take time out of whatever is important to you to look at it, there's something wrong with you! This was in Washington D.C.; if you're American, most of those people in the station are running your government, and here's this guy distracting them with a violin! I imagine a smartass artist response to this would be, "Exactly - their lives are out of balance." Next time this same hypothetical smartass is running somewhere, to their job or to pick someone up at the airport or to meet someone for lunch, let's take ten minutes of their time and ask them to just calm down and listen to some Miles Davis before they jump in the car, and we'll see whether they're concerned with balance then. The point is, there are lots of people who enjoy Joshua Bell and classical violin, and when they want to, they go to the symphony and do it there, on their schedule, when they're expecting to. Not completely out of context when they're trying to do their jobs.
To reiterate, Bell was gracious and brave to undertake such an experiment, as was Weingarten to approach him - but the article is better as a starting point for surfacing the assumptions we have about the esthetic demands that high culture makes on our attention.