Before you could download licenses for everything you owned even without the game being installed. Now you must install a game first before you can get a license for it. This will have major implications for jail breaking.
It is a PC. In fact, a good PC. It runs Linux. But it's better than a ordinary Linux PC, since it also has an amazing console UI that's actually fun to use with a gamepad. It's the best of both worlds, and it's build on top of FOSS software. It's excellent.
The console UI is just the Steam Big Picture mode but unlike desktop Linux is loaded into at startup. Although loading it at start up can also be enabled on Linux desktops even if you aren't using SteamOS.