One thing to add - he's not totally off base about the 400K price tag. If you could earn 50K/year as a high school grad, that's 200K in lost earnings (though it would be taxed). Stanford's tuition is about 40K/year now, right? So there's another 160K. Not too far off (I wouldn't count living expenses, because those would be incurred regardless of whether you were in college).
A high school grad with no skills isn't going to earn 50K a year as a dishwasher. But someone smart enough to get through Computer Science at MIT might easily blow through the 50K/year estimate. So the opportunity cost could actually be much higher than 400K.
I think including potential wages is at least a little weaselly. Besides the fact that you can work while going to school, get scholarships, etc, you could just as easily say that any lost earning potential while taking classes should quickly be made up by the difference in your wages from having a degree.
Even if you do, 50K/year as a high school graduate (at least in the US) is being pretty optimistic. I don't think most of my friends in non-technical programs didn't even make that out of college. The average starting salary for a BS CS grad even is probably still only around 50K.
This is why the right answer is "it depends". And it's why I liked the original article, even though I disagree with the conclusion that college is a waste of time. It might be a waste of time, it might be useful but not worth the cost, and it might be enormously useful and well worth the cost.
I have a feeling a really good hacker who can do consulting work, or join a startup, could easily earn more than 50K, and might be ahead of college grads by the time they do enter the workforce. Think of it this way - you might make more with PhD than a BS, but you won't necessarily earn more than you would with a BS+6years experience, and even if you do, you have to account for lost earnings.
Of course, High School only vs. BS is a very very different equation from BS only vs Ph.D. Personally, I do think that smart people who want a career in a technology related field would be well advised to attend college.
A high school grad with no skills isn't going to earn 50K a year as a dishwasher. But someone smart enough to get through Computer Science at MIT might easily blow through the 50K/year estimate. So the opportunity cost could actually be much higher than 400K.