I'd divide those who want to learn WebGL into three groups:
Those who already familiar with OpenGL (so-called “Big OpenGL”).
Those who don't know OpenGL but know some other low-level 3D graphics API, e.g. Direct3D.
Those who are completely new to 3D graphics.
Strictly speaking, when writing tutorials, a special approach should be used for each of these groups. However I need to put everything in a single tutorials set, and make it not too complex for those who are new to 3D graphics, and not too boring for those who have mastered some 3D API already. Not an easy task, you know :)
I will do this as follows: if some lesson will give nothing new for an OpenGL guy then I will begin it with “If you're already familiar OpenGL then you can skip this lesson”. And something like that for Direct3D guys.
There are some 3D graphics related topics that should be covered to learn how to make a simple video game. For example: how to use 3D models created in CAD software like 3ds Max or Maya in WebGL, or how to do a skeletal animation. These topics are out of scope of WebGL tutorials. I'm planning to write such set of tutorials in future.
And we can move on to the WebGL API basics.