Incorrect. I am fully aware of the 2-stage shutter key. But pressing the key half-way does NOT put the camera in continuous auto-focus mode. It merely lets the camera focus on the center of what you are CURRENTLY pointing the camera at when you press it halfway. It's the exact same system used on the Nokia N8. Meaning once you press it halfway and the camera focuses, you must take a picture of what you've made the camera focus on, if you choose another scenery while its pressed and the disparity in distance is too great, your picture will come out out of focus.
Pressing the 2-stage shutter key is almost exactly the same as touching the middle of the screen to take a snap, except with a slightly wider focus range in the middle. The iPhone 5 however, has true continuous auto-focus, meaning while the camera is active, it continually refocuses as you move the camera around when trying to pick a scenery. It's always there, always ready to take a picture for you as soon as your finger touches the snap icon.