the first two demos I posted are actually made with pure javascript, and it was quite a while ago. I mainly wanted to see how advanced webgl was (and it was pretty buggy at the time).
the skinned meshes are done using bone animations with matrix transformations. the billboards are done using a shader pseudo instancing so there are no changes to the vbo at all.

I also agree that for any serious projects for mobile devices, javascript is just not fast enough. so it's best to be able to do both the javascript and the native binary.