Matt Welsh, Eric Brewer, Jeff Dean, Sanjay Ghemawat, Mike Dahlin all have PhDs and lead teams that write serious production code at Google. Ion Stoica and Hui Zhang have started technically heavy networking startups. Joe Hellerstein has a new startup (I'm not familiar with the details).

You don't hear much about them because they aren't sexy consumer facing startups of the type that HN is obsessed about. They typically focus on unglamorous but technically challenging problems of the kind that require deep expertise.