Apple only expose the OpenGL bindings via Cocoa. There are many libraries that will expose OpenGL for you. [SDL](http://www.libsdl.org/) and [GLFW](http://www.glfw.org/) are the two most prominent.
Exactly. With Go and GLFW I could write 3D GL apps running the same under Linux, Windows and Mac OSX. No need to mess with OS-specifics if you don't want to. SDL could do the same but since I didn't need Audio and all kinds of "media layers" and what not, GLFW seemed a lot leaner and immediately worked "out of box", too.
You misunderstood him. He's not saying "only cocoa exposes gl", he said "cocoa only (as in just) exposes GL, but other cross-platform libs also expose it for you if you prefer not to deal with cocoa".
