The section on stack ranking is really fascinating ... seeing how that sausage was made would let you know exactly who is in the secret cabals the handbook says don't exist ;-)
I recommend looking at companies hiring pages to get a pulse on their longer term direction and strategy (a major reason for bogus job posts btw).
Based on Valve's [0], it's mostly sustaining work for Steam Marketplace, Steamworks, and R&D for VR.