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.
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.