Imagine some kind of angry birds or worms (think of physics simulations, means: Stability and speed will be needed)
How would you do it, when it comes to platform independent free to play player vs. player with in app purchases and premium accounts via internet?

Would you use a different codebase for every platform (PC, Mac, iPhone, iPad, Android phones...) or would you go the HTML5 way? HTML5 seems to be easier, but will there be performance / security problems?