You cannot possibly earn a billion dollars. That money is the excess labor value of Valve workers. In the context of how our society is currently structured Gaben certainly isn’t the worst of them, but he’s still a member of the parasite class.
Most of Valve’s money comes from taking a 30% cut of all sales through the Steam store, which is a lot of money. They’re not abusing their market position as much as they could (e.g. if you buy a Steam key from anywhere else, like a key in a physical box at a physical store, or another online key retailer like Humble Bundle, Valve gets no money, as the publisher can generate as many Steam keys as they want for free), but it’s the surplus value of the labour of employees of other companies that Gabe Newell accumulates.
Isn’t valve considered an amazing place to work at in the gaming industry?
I’ve heard that, yes, but that doesn’t change the fact that the relationship Gaben has with Valve workers is inherently parasitic. He may be a “good boss,” but he’s still their boss, has ownership of all their work, and could fire them at will.
Also worth noting that most of Gabe’s (and Valve’s) value is not based on anyone at Valve’s work, but instead based on taking a cut from every dev that sells on Steam. Valve is effectively a landlord renting out digital real estate. The fact that they’re able to make obscene amounts of money suggests to me that maybe rents are too damn high.