It's not quite up to iOS or Android 4.1 performance, but it's running on far less powerful hardware. It definitely feels better than the initial releases of Android in terms of responsiveness.
> Give me an example of one app out there that's in the same ballpark of quality as the stuff you can find on iOS or even Android.
The HTML5 version of Cut the Rope works pretty great on Firefox OS; the experience is effectively identical to Android and iOS.
Technology evolves and in time hardware improves to a point where the performance difference between native code and something that runs through an intermediate layer is not noticeable in a user interface (although there will always be a difference, it just wont be be relevant any more).
The mobile web rendering performance might never hit the 0-grade latency standard where we put native, but it will eventually get so close to it as to not make any difference whatsoever to anyone but cold-hearted scientists the likes of whom whish they could keep their science drinks at absolute zero chilly bins.
If your argument is more in the line of why do games keep getting bigger and meaner, needing more resources, when we could have stopped advancing 3D a decade ago and every computer would be able to play any game today; then that's a whole other discussion. But I like the path towards true virtual reality with photorealistic graphics.
Here are some other high quality HTML5 games:
http://worldsbiggestpacman.com/ http://www.wordsquared.com/ http://www.pirateslovedaisies.com/ http://browserquest.mozilla.org/