It takes about a tick for the cpu to talk to the gpu. If you do that every frame it will decrease the frame rate at least by half. If there is any animation it will further decrease it.
That's what happens in Flash, and that's what happens in Html5 Canvas.
If you optimise the process well enough you should at least expect rates of about thirty fps which is playable, but again its very optimised in the runtime, game code, and assets.
Even then you are very limited in what you can do, like a few hundred things on screen vs a few thousand.