>'Very acceptable' speed isn't what consumers are looking for when comparing battery life and wall-clock performance between competing platforms.
Where does the idea come that V8s and co very acceptable speeds come at the expense of battery life and wall-clock performance???
Not to mention that people are using far less capable web apps in the mobile and desktop space now (i.e pre-asm.js javascript), so the increase in speed due to the asm.js/optimisation standardisation would only make battery life and wall-clock performance better.