Google is not flat, and was the best company to work for in 2012 [0] because of how happy their employees are. In addition to meeting your made up measurements, significantly more people associated with Google have become richer than at GitHub; Google has made billions more money than GitHub; Employs more people; has more products; etc; etc; etc.
Flat works in small companies. It is impossible once they get above a certain size. They cannot be "more successful".. because they will eventually need to restructure as they grow larger.
You don't need to be "flat" for people to be happy, but you do need a decent amount of employee autonomy. You probably need some big-picture direction at 1000+ employees, but you don't need the closed-allocation "you work on this project, or you pack your bags" extortion of most companies.
Some Googlers have autonomy, some don't. I don't care to get into this discussion because for all my criticism of it, I really admire Google (the engineers and the vision, if not the middle management and HR) but I'll just say that the Googlers who've established a basic autonomy are very happy. They pick their projects and have little interest in leaving, unless to do their own startup. However, there's an underclass who face manager-as-SPOF and live or die by their "calibration scores". For them, Google is a closed-allocation company and these people are not happy.
You don't need "flat" structure outright, but open allocation is non-negotiable in technology in 2013.
Flat works in small companies. It is impossible once they get above a certain size. They cannot be "more successful".. because they will eventually need to restructure as they grow larger.
[0] http://money.cnn.com/magazines/fortune/best-companies/2012/s...