[IanDrake]

I don't understand why the back isn't all glass or all aluminum. The two seams on the back don't appear to be functional or visually appealing.

Can anyone explain what the deal is?

[dmishe]

Here's a good write up http://thetechblock.com/the-unibody-iphone. It's for WiFi/GPS.

[deveac]

The two glass sections contain various antennas which have signals that cannot pass through the aluminum well.

[yskchu]

Some have said it may be to improved antenna/wireless comms performance

[w1ntermute]

Just a guess, but could it be to alleviate previous reception issues?

[dakrisht]

Interesting point.

I fully agree with the OP here, the back looks bad. I don't get it. The all-glass back on the 4S was really nice. Had a certain allure and design sense to it.

Apple this time around:

Tim Cook: "Hey Jony, let's make the back uglier by anodizing the steel and let's see how many we can sell before we release the 5S next year."

Jony Ive: "Alright Tim, I bet we'll sell more than the 4S with an uglier case, you're on"