Well, let me shine some light on that by telling you what Canvas 3D is.
Canvas 3D is OpenGL ES 2.0
No, really. That's it. End of story. (What? You want more?)
OpenGL ES 2.0 is a hardware-accelerated drawing library
The 1000x speed difference mentioned above? That's the difference between doing something thirty times per second vs. doing it once every thirty seconds. The difference between unbearably slow and smoothly animated.
And OpenGL ES 2.0 is an open standard that is relatively well documented, and is actually used by numerous developers the world over (shocking, I know.)
For example, Google's Chrome browser uses OpenGL internally to do its drawing. Mac OS X uses OpenGL to do some of its fancy desktop effects. Adobe Photoshop uses OpenGL to accelerate its image filters. Adobe Acrobat Reader uses OpenGL. Most multiplatform games use OpenGL. Your fancy new cellphone likely uses OpenGL for smoothly zooming and panning between your photos.
OpenGL is not VRML
The difference between OpenGL and VRML: You give both your geometry and textures. OpenGL draws what you tell it to draw, when you tell it to draw. VRML draws what it wants to draw, when it wants to draw.
It's like the difference between an oven and a breadmaker. Sure, you can bake bread with both, and it's generally going to be easier with the breadmaker. But perhaps, just perhaps, you might occasionally want to bake something other than bread.
And it's a heck of a lot harder to build a breadmaker than an oven.
Rain on the parade
First off, OpenGL ES 2.0 is a very low-level API. You need something like 500 lines of code to get a lit spinning cube going. That includes writing your own matrix math library and a lighting shader. So if you just want to put a dancing teapot on your web page, wait for a convenience library to ease your pains.
And third, you still need something else to take care of advanced audio (as I kinda doubt the audio-tag is cut out for that.)
Oh, the future is perfect and diamondoid!
But, knowing the obstacles means knowing your goals. Making the JS garbage collector less laggy and writing an OpenAL binding might actually make writing quite impressive action games on the browser a real possibility.
It's still early days for Canvas 3D though, let's see how it unfolds.