Hmm. I'm inclined to believe this is unfair to people who might be just as competent and productive as those whose work is "out in the open", but can't share or reveal anything for some valid reason.

This is common inside the Valley and outside it. Around here, a certain fruit-based computer company advises its employees not to reveal specifically to outsiders exactly what it is they work on. People who write code for big, technical but non-software firms (defense contractors etc) similarly have nothing to show (publicly) for their efforts.

It's nice to imagine that everyone works for some fun little startup that lets you blog and contribute to open source and has everything up on github, but the reality is that if you limit the search to those candidates, you will find the talent pool pretty insular. Some highly competent and very desirable people are locked away in big companies where they're not allowed to make a big fuss about what they're doing. For them, the traditional resumé is still very valuable.