Unlike the current iPhones, iPad's sides are hard edged as well. The "crease" from the border of the iPad to the back of it is a very hard, un-smoothed edge, as is the crease on the front (see the far right http://www.miproconsulting.com/blog/wp-content/uploads/2010/... it's only bulbous because they need space for the guts -- the actual point where the back meets the border bezel is a hard edge).

Despite the way they got stereotyped with the bondi-blue iMac (ten years ago!), Apple tends to not actually like super bubbly or round industrial design, as evidenced in the shapes of all of their displays, notebooks, Apple TV, Time Capsule, and the current iMac family. Bringing their phones in line with the "its a metal border with four rounded corners, containing inset glass on the usable faces" would be 100% in tune with the rest of their current aesthetic. iPhone is currently the weird exception, especially with the plastic backs they have right now.

Also see: http://daringfireball.net/linked/2010/04/18/apple-ceramic-pa...