The smoothness and speed of ios is actually smoke and mirrors.
ios uses a lot of tricks to make things appear smoother.
Even wonder why each ios app always launch with a static image instead of going straight to the app?
That's because rather than loading the actual app straight away, it loads the static image first, show it to you, and then load the actual app.
If you time ios app load time until it gets to the actual app, it is actually slower than android.
An even easier test, load up engadget.com or any complex website in full desktop version. Now, try to scroll up or down really2 fast in ios, you might think it's smooth but it is full of checkerboard pattern, And this is true of iphone 4 in ios 4.1
IN android, if you scroll up or down really fast, the scrolling will be slightly choppier but you can actually see the content.
The same thing with zooming in and out.
Again it's all about smoke and mirrors, and I myself prefer the real thing anyday...