My iPhone 5 is considerably smoother and faster than my iPad 3. That's surely also related to the iPad's insane pixel count, but the iPhone also loads and switches apps faster, before CPU-based rendering is a factor.
Note also that he's got his canvas set to half the CSS size, i.e. each canvas pixel is 4 screen pixels on a normal display. On a retina display each canvas pixel will be 16 screen pixels. So if you tried to manipulate real pixels this way on those devices it wouldn't be pretty. (Retina version: http://jsfiddle.net/RFLaW/)
