Earlier predictions that said that the iPhone 5 would not have an NFC chip, despite the inclusion of Apple's own mobile payment system (Passbook) were based on the iPhone 5's expected metal back. AnandTech said:
"Given the primarily metal backside of the new iPhone, it's highly unlikely that NFC is in the cards for this generation. In fact, given the very little space at top and bottom dedicated to those glass RF windows, you can almost entirely rule it out.
"It shouldn’t need saying, but having a huge ground plane (the unibody metal back case) in the way of your NFC antenna will seriously degrade performance, thus only the top or bottom windows are logical places to put it."
Jim Dalrymple, who is famous for his confirmations of such rumors, and is generally right, blessed the assertion with his typically simple "Yep."
Will Strauss, an analyst of Forward Concepts, a research firm that follows digital signal processing and chips confirmed the problem:
“NFC employs lower-frequency operation than cellular, requiring a longer antenna,” Mr. Strauss said. “That antenna is often wrapped around the battery in some cellphones, but a metal back shields any radio waves from reaching a nearby data terminal. Only plastic, Kevlar or similar backings will allow the radio connection for mobile payments. Clearly, Apple chose beauty over functionality with its aluminum back.”
During its introductory event, Apple announced that the new iPhone design was glass-and-aluminum.
While another explanation could be that Apple doesn't feel NFC is ready for the market, that seems unlikely, based on the addition of Passbook to iOS 6. Still, it is true that NFC is very new, especially in America.
Google's own Wallet system has yet to take off.