WebGL is “OpenGL ES 2”, not plain OpenGL (the ES stands for ‘for Embedded Systems’). So there’s the first difference. OpenGL ES is essentially a subset of OpenGL. In addition, WebGL is almost the same as OpenGL ES 2, but has some subtle differences, explained in the link you provide. There’s not much to add to that link, it’s a pretty clear explanation of what is different between OpenGL ES 2 and Webgl.