[Apologies if this should go in Open Topic, I wasn't quite sure.]
I was just reading this interesting paper by the creator of Aquaria, who also ported the game to ipad. It shows that, as we know, graphics performance on mobile is largely limited by the pixel fill rate.
One statement in particular interested me. Even in a native app, the latest ipad can only draw 4x the size of the screen and keep a steady rate of 60fps (not counting overhead performance). Ashley has been telling us this all along (but we keep complaining!), along with the fact that native developers often use optimization tricks to make the games run faster. This paper shows one such example.
The paper goes on to state that 2D games with hi-res art (pretty much all C2 games fall into this category) are as such very hard to make as they don't take full advantage of optimized 3D graphics processing in such devices - they suffer from overdraw as graphics are laid on top of each other - even transparent pixels have to be drawn!.
The rest of the paper describes how the developer essentially 'cuts out' every 2D image and puts them on a 3D 'canvas' - using the 3D technology so that overdraw is no longer a problem. He reports significant performance benefits.
Obviously something like this would be non-trivial to integrate into C2, probably even impossible (maybe once webGL becomes more widespread). However, it gives a good perspective and shows us that HTML5's mobile performance isn't as bad as we think.
(Please correct me if my ignorance caused me to butcher the facts!)