Thoughts on chamfering
I've used an iPhone 5 for more than 2 months now, and an iPad mini for about 2 weeks. And I think I've figured out why Apple added chamfered edges to both devices.
Yes, the polished edges add an extra bit of shine, and yes the chamfering process made for a good talking point during the iPhone 5 rollout presentation ("polished with crystalline diamonds"). But I think the actual function of the chamfering is to give you a more secure one-handed grip. It creates two relatively sharp edges, each generating lots of friction against your thumbprint. Better for one-handing the iPhone 5 and iPad mini.
Try (carefully) holding an iPad mini, face up, with one hand. And don't fan out your fingers like a waiter holding a tray. Just grip it by one edge, thumb on top. Now see how far you can move your thumb off the screen without dropping it. (I told you to be careful! Put your other hand under the thing to catch it.) Pretty impressive how little thumb you need, isn't it? You should be able to easily hold the mini securely without covering up any of the screen with your thumb.
Now try that same grip with the iPad mini face down. Your thumb will be gripping the rounded back edge instead of the sharp chamfering. You'll need more thumb. Way more. And it will be far less predictable. Very hard to tell when it's about to slip. A rounded top edge would probably lead to more dropped iPhone 5s and iPad minis.
So why does the iPhone 5 have chamfers on the back? Because there are two glass antenna-port panels on the back. It would have been very difficult to make rounded glass panels to match a curved back like that of the iPad mini or iPod touch. And because the iPhone 5 will be used one-handed often, every extra bit of grippiness will help avoid a drop. One-handing an iPhone 5 and snapping a photo using the volume-up button as a shutter release is a great example of when maximum edge grip is needed.
I wouldn't be surprised if Apple updates the big iPad with chamfered edges on the front. But it would only be a decoration. No real need for it unless Apple slims down its bezel too.