I don't see why this might as well not be the default, if more browsers' source view would just de-minify CSS/HTML/JS automatically.

EDIT: Especially in mobile/touch-only browsers who are extremely unlikely to inspect the code. So do it for m.example.com, I reckon.

I myself have gotten a little lazy, because I'm hosting my static websites behind CloudFlare who do minification anyway, so I haven't thought much of this in a while.