I think that there is easily a 10x disparity in output divided by hours worked. Why did the Etherpads just make 8 figures over the past 3 years, while I made only 6 figures? They certainly didn't work 100x more. By the economist's definition, they were easily 100x more productive.
I think that there's a more interesting question in the article - why do salaries "flatten out" the productivity curve, so that programmers who would easily be making 100x more as startup founders are instead making 50% more, with the balance going to the employer? After all, if we measure by revenue generated for the employer, I'm in at least the 7 figures, within an order of magnitude. And I doubt Aaron etc. were making all that much in salary when they were Google employees either.
I suspect the answer to this has to do with risk allocation. Because technology markets tend to be winner-take-all, there's a lot of variance in productivity that's not the result of the coder's actions. In other words, it comes down to luck, being in the right market with the right product. You can work hard at the wrong thing and still produce nothing of value, despite being smart and dedicated.
When you sign on as an employee, your employer agrees to take on the risk that you'll work hard and still nothing will come of it. And in return, they get nearly all of the upside if your hard work does result in something great.
I suspect that the 10x more productive figure is a result of sample bias: when you look at what people have done, there are some folks whose projects were 10x more useful than what other people have done. All the people who worked equally hard and produced equally large amounts of code are lumped into the "not productive" category, because in hindsight, their projects weren't all that useful. If you try to predict, a priori, who the 10x coders are, I bet you'll have a much harder time. If you don't, you have a sterling future ahead of you as a venture capitalist.