If you search for “Away3D WebGL”  or “Stage3D webGL”, this is the first result you will get:
http://www.airtightinteractive.com/2011/10/stage3d-vs-webgl-performance/

from the benchmark, Stage3D+Away3D is much slower than WebGL.

And when I tested it with Adobe Scout, I found the major issue is in: 
Context3D.setProgramConstantsFromVector() is called too many times in every frame and it takes 40% CPU time.
and Context3D.setProgramConstantsFromMatrix() takes 18% of CPU time

This doesn’t make much sense, since there are games with more complex logic that still run smoothly.

Is it a bug in Away3D 4.0 ? or this guy use Away3D in a wrong way?

The examples that Felix did are using the early alpha version of away3D code named Broomstick. Lots of water has passed under the bridge since then.

I fixed his source code and compile it with latest version of away3D.
but the framerate is same as the original one.