First, there's the obvious: the article talks about the difficulty in locating programmer candidates that can perform basic programming assignments in an interview setting. Several commenters hit on some of the things that can contribute to this problem, including the psychology of an interview environment, the ability of the candidate to manage their stress, and the obvious problem that there's a lot of CS graduates who haven't spent enough time behind a keyboard to be useful in a production programming shop. That's what his article is about, and I'll leave that discussion there.
I'm much more interested in the response to the article. Responses range from senior developers to folks still in college or high school, and the resounding pattern is: they want to solve the problem. That's not what the author was shooting for, obviously, but readers were falling all over themselves (myself included) to post up the first response in their favorite language.
My speculation is that programmers who love what they do - the kind of folks who hang out on programming-related websites, who read the latest O'Reilly books when they come out, who participate in open source projects and "scratch itches" regularly - can't ignore an opportunity for practice, much like what Dave Thomas talked about when he introduced his idea of "Code Kata". Throw out the accusation that most programmers can't solve a simple problem, and you've practically demanded that they take a swipe at it.
There's more to it, though; lower the barrier enough, and more and more people get attracted to the idea. You see this kind of behavior on topical mailing lists: ask a complex question, and you may get an answer, but not a lot of people will jump up and offer their help. Ask an easier question, perhaps something that a lot of people know the answer to (or can easily derive the answer to), and suddenly, you get an overwhelming response. There's an aspect of ego at play here that's interesting; it's an opportunity to present yourself as a subject matter expert, or at least as someone knowledgable of issues surrounding the question.
Interesting stuff, to be sure. I suspect there's a good group dynamics case study or paper to be had here for someone with the time.