"use asm" is not a keyword. It can be ignored, as V8 does. This is possible because asm.js is JavaScript as defined by ECMA-262. It executes according to the semantics specified in that document.
I don't really want this to turn into a back-and-forth, but it's unfortunate that this has devolved into outright accusations of dishonesty.
Note that I framed it as "not exactly honest" rather than saying it's an overt lie. Because I don't consider it an overt lie, but it's hard not to read it as a bit equivocal to claim that asm.js as just JavaScript.
And really, I'm far more concerned with the future plans, particularly with regard to things like multi-threading APIs. I don't see how those can be incorporated in a way that supports asm.js as an easy target for existing code while not causing it to diverge from JavaScript as used in the browser.
To be clear, I really do think those of you working on asm.js have the best of intentions and really want to make something that works for the Web. However, I expect that supporting existing codebases and commonly used APIs is going to mean compromises. They'll start small and polyfills will work well enough, but I just don't see how asm.js doesn't eventually diverge in significant ways from normal JavaScript, or end up introducing special purpose hacks. Maybe I'm wrong, but I don't see my position as unrealistic.
I don't really want this to turn into a back-and-forth, but it's unfortunate that this has devolved into outright accusations of dishonesty.