actually

Perhaps because the design of those features were backed up by statistical improvement metrics? http://blogs.msdn.com/jensenh/archive/2006/04/11/573348.aspx

The AXiS49. http://www.youtube.com/watch?v=C9-OSCl7kOc

It's like cheating at music.

It is software rasterizing, written in haXe. I know the author from his posts on the haXe compiler ML, so I have a few details about the engine. haXe itself compiles to JS/C++/PHP/etc., however the only way that engine could possibly be fast enough is to make use of haXe's Flash-specific "Memory" API, which uses opcodes from Adobe Alchemy to manipulate a flat memory space at the byte-level.

While it could definitely be ported, you'd have to change the part of the implementation that makes it fast to do so. If JS got a similar ability to do byte-level manipulations, it wouldn't be out of reach, but right now it looks like JS implementations are avoiding these kinds of proprietary extensions.

For comparison, what Flash can do now: http://www.badsectoracula.com/peponi/rayfaster2/

I would guess it's more like "pump white noise to an infinite number of people's ears at the press of a button."