I'm not sure how that follows from the data. I'd be more likely to conclude that the job market doesn't support the levels of college graduates being produced.
I've often heard it said that the fundamental problem with economics is that it assumes people are rational and have good information. I'd say it goes deeper than that: it assumes that money is the rational thing for a person to maximize. In reality, money is something that bears some maximization, but it's hardly the primary consideration.
Considering that, it's clear why we'd use money as a proxy. Not a perfect one, of course.
Labor supply theory, for example, assumes people maximize utility by choosing a combination of work and leisure. It doesn't assume people work as much as possible (or, maximize their money).
First, it seems to write off any sense of plasticity in cognition and learning.
Second, these people clearly were successful in that they earned a degree, so ojbyrne is right in that this statement and the data have no correlation; say what you will about the quality of an education in some institutions, but I can assure you that plenty of people in food service and janitorial occupations dropped out of college (if they were fortunate enough to have the opportunity available).
Finally, it underscores the article's implication that a lack of success invalidates the reason for having tried at all. As other commenters pointed out, a college degree can be a vehicle for personal fulfillment, salary maximization, etc. (There was a link on HN very recently about the 100-year-old man going for his PhD... is his effort not worthwhile?) Call me crazy, but I believe people who attain a degree are enriched in some way, and if they fall short of their original goal it's still better to have tried.
I work for an education-related startup, and I'm quick to acknowledge that problems abound in higher education... but this article really raised my hackles.
If we as a society are contributing money and other collective resources to make higher education possible, yet more than half of the young people dropout, then it's pretty clear that most of them do not have the "abilities" to succeed at higher ed. However, it is far more likely that higher-ed itself is structured completely wrong. If the system fails most people, then most people are not failures, but rather it is the system itself that is the failure.
Granted it is highly debatable what "abilities" refer to, and what "success" entails. Both are mostly arbitrary markers which will be wildly different for everybody.
I tend to view things from a different perspective—I'm a cheerleader for the notion of the classical Liberal Arts education, and learning for the sake of becoming a Better Fucking Human Being, not for the purposes of some phony job in a phony society performing whatever phony crap those in power have commanded.
By disengaging education from mere financial concerns, my biggest problem with all of this is not that we have thousands of massively underemployed people, but that we have the social expectation that the most educated deserve to be the big shots, manage everything, do little real work, and collect most of the profit just for showing up. Sorry, in this society, you only get those entitlements by luck of birth, inheritance or marriage. Just going to fucking college and earning a piece of paper does not automatically grant it to you.
Entitlement is really what this article is about, but the author can't just come out and say it, because that would piss off his audience even more than his Bell-Curve innuendo. (Don't even get me started on why some of the most entitled people are incapable of acknowledging it, and pretend otherwise). Many academics are outraged that their so-called highest achievements don't guarantee a high status role in society outside of academia. But the truth is that the value of education and learning is insignificant if you're measuring it by economic metrics. And society at large worships wealth and fame. Just because you have an encyclopedic knowledge of Proust doesn't mean you deserve jack shit from society. Even though there is no way in hell anyone could read Proust and not be enriched and transformed as a person in incalculable ways.
This whole article and debate is really an Apples-versus-Oranges false dichotomy, and I'm not sure why I got suckered into writing this long reply. :P
tldr; Being really smart and highly educated should have little to no correlation to your social & financial status in society.