Let’s take another look at the official Khronos definition of WebGL (the italics are mine):
Obviously this is a mouthful, so we’ll have to forgive the writers for trying to fit it all into a paragraph. But it’s possible that the Khronos folks have—to borrow a term from journalism—buried the lead here. Look at the text in italics. In my opinion, the true breakthrough unleashed by WebGL—what really makes it different from any other technology that has come before—lies in its ability to be seamlessly integrated with all other content on the page.
3D graphics has been around for a long time. Even 3D graphics in a web browser ...