This is a rather common phenomenon: It's called "simultaneous invention," and it happens all the time: Technology advances to the point that the next step is obvious to multiple people, and so they all take the next step at approximately the same time. In the end, one of them gets the patent, or the market share, and so squeezes the other out and becomes synonymous with the invention. That's what happened with Alexander Graham Bell, who in all likelihood invented the telephone after Elisha Gray -- and both of them came after Antonio Meucci. Amusingly, the discovery of "simultaneous invention" was another case of simultaneous invention, with multiple thinkers and researchers publishing on the phenomenon all at once. "Unjust Deserts," by Gar Alperovitz and Lew Daly, has a good discussion of this....
In other words, the difference between Mark Zuckerberg and Adam Goldberg was very small, while the difference between Mark Zuckerberg and the smartest college kid in 1999 was huge. It was the advancing storehouse of human knowledge, not the advancing capabilities of particular humans, that made up the difference. But humans tend to think about things in terms of other humans, and so we overestimate the impact of personalities (autistic genius) and underestimate the importance of technology (all sorts of people could suddenly build social networking platforms in under three months). That also makes it easier for us to believe people deserve* enormous, inconceivable monetary rewards for their inventions, as we tend to attribute the entire value of the product to them, as opposed to attributing the incremental difference between that product and whatever was right behind that product to them.
*Note the word "deserve." There's a different argument that assuring people astronomical profits for creating useful things makes them more likely to create useful things. That argument makes more sense.
This bit of misunderstanding, with the help of Ayn Rand and her acolytes, last year mutated into the deeply stupid idea of Going Galt, in which our leading innovators, in response to TARP, all go on strike and allow society to collapse without them. So if Mark Zuckerberg--the youngest billionaire ever, eminently deserving of all his fortune, and even more virtuous for not asking for money from Facebook's parasitic users--withdrew from society, and even took Facebook with him, then there would follow a great gnashing of teeth, and a great void would open in our lives, and absolutely no one would think or be capable of swooping in to fill the newly opened niche.
Makes perfect sense.