My point is that regardless of if a 4S shot better photos, the photographer could hiccup and get a blurrier photo than they might have taken last with a 3GS. In a less extreme circumstance, they could have just exhaled instead of hiccuping, in which case no one would have noticed and the error could be incorrectly attributed to the camera.

A great photograph with a camera phone requires a certain set of parameters that can almost entirely be individually measured outside of human interaction (and randomness). If you want good handheld performance, you need a fast exposure time, which can be measured from the EXIF data of each photo. If you want high dynamic range, measure the ratio of pure white and black pixels to the rest of the image (white and black is basically over/underexposed). The only thing that would be effected by motion that I can't think of how else to measure beyond being handheld is time to good focus (outside of crazy contraptions that result in more repeatable motion, like sticking your phone in a centrifuge), but there probably exists a way to do so while avoiding the inherent non-repeatability of humans behavior.