In Mavericks, when I'm running a full screen game, the second screen can't show desktop (or browser, or anything else.) My understanding is that Mavericks sets the second screen in a different Space so both can be used. Am I doing something wrong or is that a wrong understanding?
I believe Steam uses its own full-screen mechanism independent of the system's full-screen option. Since it's not the typical full-screen provided by OS X, the multiple spaces feature doesn't work here.