In nearly every case when a game is released on console and PC, the console versions sell a tonne more copies. Like, it's not even close. Unless we're talking about a Valve game.
While the developer, publisher and operator of Steam sadly never releases internal sales figures for its online marketplace, Valve boss Gabe Newell has told Gamasutra that while the Left 4 Dead series has sold much better on console than on PC, "Portal 2 did better on the PC than it did on the consoles".
We'll probably never know just how much better, but the fact it did better at all is a feather in the PC market's cap. And maybe a sign that, hey, when developers release games that work well and look great on PC, instead of being shitty ports or being saddled with crippling DRM, people may actually buy them.