John Gruber:

On the iPad, the thick bezel area sur­round­ing the dis­play serves an essen­tial pur­pose — it gives you a place to rest your thumbs while hold­ing the device. The non-display “fore­head” and “chin” on the front face of the iPhone serve no such prac­ti­cal pur­pose. All Apple needs is enough room for a home but­ton at the bot­tom, and the speaker, cam­era, and prox­im­ity sen­sor at the top.

No. The width, in land­scape, of the fore­head and chin of the iPhone is roughly the thick­ness of an aver­age thumb. And both have iden­ti­cal widths; they are sym­met­ri­cal. My guess as to why there are such thick top and bot­tom bezels with roughly the thick­ness of an aver­age thumb is: So you can grip the iPhone with your thumb, left or right.

Think about how you hold the iPhone when tak­ing a photo. I find my thumb need­ing that fore­head or chin to hold on to. That thick bezel also comes in handy when I’m play­ing games, espe­cially games where you need to tilt the iPhone to turn left, right, go fast, or slow down. The fore­head and chin of the iPhone serve impor­tant prac­ti­cal pur­poses, and will not go away.