Currently, difference in performance between asm.js and WebAsm is about 5%. It doesn't looks like performance gain or portability are main reasons to select WebAsm over JS. IMHO (I'm developer myself), main reason is better obfuscation of the code.
I don't know of any programs that are distributed as C to be run directly like javascript.
> Machine code donesn't move needle of obfuscation much at all
There are two very fundamental mistakes you are making when equating webasm to raw processor instructions. The first is that webasm even its binary format is still organized in a abstract syntax tree, so its instruction are not flat, they are in a hierarchy.
The second is that webasm doesn't take care of the input and output. Right now it doesn't even interface with the document object model, so all the IO is still done through javascript.
Also, I don't know how you think there's a noticeable difference of readability between minified asm.js and textual wasm for the average person. It might be more difficult for a programmer to read the wasm, but I can't imagine that "disassembled" asm.js is particularly readable in the first place (and both are completely incomprehensible to a non expert)
Average person see no difference at all. Moreover, I tested tank demo right now, and asm.js version is about 6% faster at loading (1.99s vs 2.12s from cache at Firefox 57.0/Fedora 26).
https://caniuse.com/#feat=asmjs vs https://caniuse.com/#feat=wasm
If you are trying to point that wasm is supported better on iOS, then look at performance tests: https://arewefastyet.com/#machine=29&view=breakdown&suite=as... . At many tests, Safari is faster than other browsers at asm.js microbenchmarks.