Comparing the EXIF data of these two images supports the idea that the iPhone 5 does have a different sensor to the 4S. The 4S selected ISO 64, while the iPhone 5 has been able to drop to ISO 50. For images taken in such bright light, this strongly suggests the newer model has a lower minimum sensitivity.
Looking at the EXIF data of the images confirms Apple's assertion that this is a new sensor, despite the pixel count remaining the same. Close examination shows the iPhone 5 is using a 4.1mm lens to give a 33mm equivalent field of view, rather than the 4S's 4.3mm lens, which gave a 35mm equivalent view. This means the new sensor is a tiny fraction larger. The iPhone 5 has also selected ISO 50, 1/3EV below the 4S's minimum sensitivity of ISO 64.
Take a look at the photos below or click here for more sample photos actually taken with the iPhone 5.