[kuahyeow]

This depends on the type of the game, but a fellow developer is beta-testing a canvas based game http://esdao.com . It's works quite well, with the exception of Mobile Safari to my recollection which is supposed to perform better with the next iOS update.

[fookyong]

no discredit to your developer friend, but the level of visual complexity that the OP refers to is far in advance the game you linked.

Here's a video of the Aves engine in action:

http://www.youtube.com/watch?v=Ol3qQ4CEUTo

As someone building an HTML/javascript-based animated game myself[1], I'm somewhat aware of the challenges involved and am frankly amazed that the OP has this level of performance coming from HTML/js on so many different game objects.

[1] http://littlecosm.com - a massively multiplayer twitter client!