Considering UE4 and Unity both support OpenGL, yes, a lot if not the majority of games.
WebGL and OpenGL ES are pretty much OpenGL. Formally they are different standards, but they are based all in OpenGL: if you know one, you know the others pretty well, which is what is important for developers as you agree in the second paragraph.
WebGL and OpenGL ES are pretty much OpenGL. Formally they are different standards, but they are based all in OpenGL: if you know one, you know the others pretty well, which is what is important for developers as you agree in the second paragraph.