Sink
Well and I have also heard the theory that the band is really a heat sink and the seams facilitate expansion and contraction. But then I'm voting that this not what the final device will look like.
I doubt that the seam would really improve shock resistance. The most plausible explanation that I've read is that the seam is a vent and allows some of the heat to dissipate.
The iPad has some heavily discussed issues concerning heat-related shutdowns.
I've dropped my iPod touch a number of times before I got a case (it's a slippery little critter), but nothing more than a couple of scratches in the metal. It's still a pretty durable design.
Well and I have also heard the theory that the band is really a heat sink and the seams facilitate expansion and contraction. But then I'm voting that this not what the final device will look like.