As the new cover is only protecting the screen, wouldn't that lead to the back of the device to acquire the scratches usually associated with apple devices?
This might lower the resale value of the device which could be another reason for the design that Apple has chosen here.
Doesn't anyone like patina anymore? A scratched up aluminium back looks good as time goes on. Same with your leather briefcase as it wears in, or your cars seats.
The iPad V1's back was very resilient to scratching. Not sure if the same is true of the V2. Ultimately any mobile device is going to get some dings. That's just how it goes.
This might lower the resale value of the device which could be another reason for the design that Apple has chosen here.