There are many games on the App Store that, like this one above (RF09), emulate a joypad using a virtual stick for the left thumb and 2 or 3 buttons on the right.
Below there is a screenshot taken from my Iphone, and above an image of another famous game X2Football
. As you can see the two interfaces are different and the first one seem to be simpler to use (less and bigger buttons) but in reality I found RF09 really unusable and frustrating! When you are playing on a plain surface, you can't evaluate where you fingers are, especially for the direction pad on the left and is very very easy to go out from the pad area: the result is that very easy to stop the player while running and lose the ball.
The developers of X2Football solved this problem introducing a simple and cool feature: comparing those two images, you will see that the left pad is not in the same position, but it automatically follow your finger and when it touch the screen, the pad goes exactly when your thumb is (check this video
for a live demo). You are not required to adapt you finger to the interface, it is the device that optimize it while playing!
On the same way the right buttons are ergonomically designed, and not just two balls.
That is a real good example of how thinks dramatically change with just a simple innovation.