>I really don't think that asm.js is necessary to bring 3d gaming to the web.

It helps ... a lot. WebGL gives you GPU access which will largely drive your graphics engine, but there's still tons of places where CPU performance matters (e.g. physics and AI). Asm.js and WebGL are complementary.

>I'm on the web to take advantage of things like JavaScript and CoffeeScript.

And asm.js prevents this how? If you're coding in CoffeeScript, you already have a necessary compile step to do. Are you telling me you wouldn't want the CoffeeScript compiler to give you extra performance by including asm.js heuristics?