There are an insane number of misconceptions about Linux in this thread. I'm going to try and address a few:
The [G]UI is bad/good/etc: Linux doesn't have a graphical interface. What you are referring to is X, plus one of: Gnome, Unity, KDE, etc. SteamOS will use none of these (unless you install them yourself, presumably). Also, X is bad, but is in the process of being replaced by a much more modern windowing server/client system called Wayland.
Short, easy version: The Linux UI can be anything.
The Linux licensing requires devs to release their source. Not true. Anything binary can run on, and link against, any library without releasing source. They only have to release source if they actually repurpose source code that is licensed such that it requires them to do so. GPL, a common open source code license, requires this. However, MIT, another common open source code license, does not require this. SDL, the code that glues Source Linux games to the OS, is under the zlib license, which does not require this.
Short, easy version: Nobody has to release source code to run on Linux => Games can run on Linux.
SteamOS is just like Windows, Valve is as bad as MS: Kind of true. At this point, Windows allows you to install anything you want, as long as it's not using their modern API. SteamOS is a normal Linux distro, which means it lets you install and modify anything. You could remove Steam, if you wanted to. This does not change the fact that games downloaded via Steam are just as DRM'd as they are on any other OS. We know Linux can never become a walled garden because anyone can fork it and fix that (thanks to aggressive GPL licensing). We can't trust that Windows won't lock out other software in the future (and this is the direction they are going).
Short, easy version: Linux is inherently trustworthy, Windows isn't.
OpenGL is better than DirectX This is not really true. OpenGL is actually a set of standards and extensions, which graphics vendors choose to implement or not as they see fit. In a vacuum, OpenGL specifications supported tessellation before DirectX did. But DirectX is an implementation, which means that they day DirectX10 came out, tessellation was there while OpenGL still just had it "in theory". However, OpenGL has been pulling itself together and getting a lot of support in recent years. Valve is helping with this.
Short, easy version: DirectX implementations are better than OpenGL implementations, but this is changing (thanks to mobile, console, etc).
Full disclosure, I am a daily Linux user with enough familiarity to set up my own GUI (X + xmonad). I'm not a typical user, and I'm not saying that Linux (even Ubuntu) is as easy to handle as Windows or OSX. There is nothing from a technical perspective that prevents this. Moreso, it's an idealogical thing. If everyone in the Linux community was working on GNOME, or KDE, etc, it would probably reach parity with Windows 7 or w/e. But the strength of Linux is also in this case it's weakness: people want different things and work on different things. Linux, when you take the time, will give you a computing experience hand-crafted for you. But you're probably not going to sit down and find top polish.