the amount of cores makes no difference when javascript is single threaded. Infact its often detrimental especially on mobile because each individual core is significantly weaker.
Plenty of websites doing advanced html5 gunk bring top of the line systems to their knees.
Ok, valid point... But still the Ghz's per core are also increasing, and with that the overall performance. If you've used webapps like Popcorn-time or Slack you'll understand what I'm trying to say.
Are they native? No, they're JS apps
Do the users care? No, cos they do the "job" pretty well
We're reaching that computing power with mobile devices. In fact current mobiles are like desktops of 3/4 years ago. For certain kind of apps it won't matter if they're built with web technologies. (I'm not saying that you should bet on WebGL vs OpenGLES)
Plenty of websites doing advanced html5 gunk bring top of the line systems to their knees.