Here at FT Alphaville we love exploring “black hole” companies: those ultra-private businesses that must largely be observed by the influence they exert on others.But even within that category, there aren’t many places quite like Valve Corporation, with its bizarre corporate structure, revenue-per-head figures that would make Silicon Valley or Wall Street giants hot and bothered, a product that seems to basically print money, and a seldom-seen leader deified in some corners of the internet — all...