Well, but depends....I mean, so much people need more performance...sometime is true, but in the most case is because people made bad process and use a bad way to make their games... in the forum I see a lot of mistake in the examples, I see a lot of bad ways to reach something...
Actually I never finish a game, I made different prototipe of some games, and they works great, my problem is how to make the gameplay/level....
I had to quit just one game because of the performance, but because I was using a lot of graphics in HD,
in the mobile, is crazy to think "I want a perfect performance..." if you want the perfect performance, you have to programm everything with the native code, that is the easiest way to make your game better, HTML5 isn't ready now the mobile game if you want to make a fancy game...
anyway, in the future will be easier to make games in html5, and the hardware can be ready for that