Try clicking one of the examples in the menu on the top, and then hit 'Play'.
Love it! It is certainly great for playing around with WebGL, but still lots of work necessary if it wants to catch up to Unity or CopperCube and create complex WebGL games or scenes.
You are right with the lack of open source state of the art engines, it is a shame.
But you are misinformed about the webgl part: There are other Web 3D engines. For example Babylon or CopperLicht. The latter even has a pretty solid WYSIWYG 3D editor: http://www.ambiera.com/coppercube/