TechDirt has a great analysis of a larger analysis on Valve’s profitability, specifically how TF2 worked when it went free. The major lessons are research, connecting with customers, make it so pay isn’t needed to play, and give people a good reason to buy (not a negative). In short, it appears to be a giant mass of common sense, which of course makes it rare and remarkable.
Well worth reading.
Also, what I’d add here is that Valve’s approaches are not based on adversity, they’re based on building alliances and providing value (as noted “piracy is a service problem.”). This is a great model that is also common sense, but begs the question why common sense seems so alien today. I’d argue that once companies get big enough to throw their weight around, and gain enough “age” to feel they’re fixtures, there’s a risk of abuse.