"We own our platform, Steam. Microsoft owns their platform. They wanted to make sure there's an economy of value there," said Faliszek to Eurogamer.
The first content release for Left 4 Dead, which included a new Survival mode and extra Versus maps, was free on both platforms. Crash Course, set to include a new campaign for the game, will be free on PC and cost 560 Microsoft Points ($7) on the 360.
"[Microsoft] helped us get the first one out for free," explained Faliszek. "We had the one DLC out for free. And I think... they have to look and say, wow, we're kind of being unfair to everybody else if these guys can do that."
Added Faliszek: "It's not like we're looking at this as, 'Oh my god, we need some money, we're going to charge,' obviously, or we'd do it on the PC. So it's just kind of the way the system works right now."
Valve will also have to put a price on its upcoming Xbox 360 Team Fortress 2 DLC pack.
"On the consoles, they want us to charge money for [DLC], because that's in their model, and our model is very much more to grow the community by giving out free updates," said Valve president Gabe Newell last year. "That's harder for us."