Why doesn't the aluminum cover all of the back?

[MultiMediaWill]

What is the point of the two tone glass and metal back? What is the issue with having the entire back completely metal?

 

[sjinsjca]

Radio waves don't penetrate aluminum well. So some of the several antennas in the phone are located beneath those ceramic plates.

 

[YungMoola94]

For the radio it needs transparency.

 

[DOUGHNUT]

Yep, same reason LTE iPads has the black plastic strip on top and MacBooks have plastic covering the hinge

 

[Blorzoga]

What is the point of the two tone glass and metal back? What is the issue with having the entire back completely metal?

Because Apple wanted there to be a little of the back that's not all scratched up.

 

[FPSDavid]

Something about signal issues if it were to have a full-metal back.

 

[sjinsjca]

Yep, same reason LTE iPads has the black plastic strip on top and MacBooks have plastic covering the hinge

Just a fine point: the 3G models have had that plastic window since the first-gen iPad. It's not just an LTE thing, it's a RF thing.