Well, that’s the “How will people know that I upgraded?” question resolved.
Joking aside, the fact the front of the iPhone 5S is visually distinct from the iPhone 5 is a big deal to normal people. It changes the perception normal people will have about the new phone dramatically.
In addition, it reinforces the fingerprint sensor gimmick factor. Friends will notice people with the new phone and want to see the new feature in action, in the same way onlookers demanded Siri demos when the 4S was brand new.