Well, I think HTML5 gaming is viable on mid to low end devices. I just also think if you have a phone which is about as powerful as a mid-range desktop, which is the state of the latest top-end phones, it would be nice to take full advantage of that - just like with a top end gaming PC you want to be able to run Crysis at 60 FPS, not locked to 30 FPS because the game designer wanted to try to improve the experience on weaker machines.