I've always suspected that OSX (and so iOS as well) was loaded with little tricks like this to give the perception of a really snappy interface. I've suspected these kinds of things were built in at the very lowest graphics levels which is why Apple devices graphics always seem so smooth compared to other brands.
Coming from windows, I always felt like when I dragged a window around that the buttons were likely to fall off! On OSX it's so smooth that I suspected they did things like take a screenshot while the window is in motion and use blurs, etc, so that all of the objects are not moving independently. I'm not sure that's actually true but what is obvious is that Apple has always been very obsessive about using visual tricks to make the UI seem very responsive and smooth.
Coming from windows, I always felt like when I dragged a window around that the buttons were likely to fall off! On OSX it's so smooth that I suspected they did things like take a screenshot while the window is in motion and use blurs, etc, so that all of the objects are not moving independently. I'm not sure that's actually true but what is obvious is that Apple has always been very obsessive about using visual tricks to make the UI seem very responsive and smooth.