That was then, this is now. The bar has been raised by Apple's CNC metal sculpture. Now they're going to shape their plastic backs like they did their aluminum backs.
And it was the glass back that set the new functional design aesthetic used for the aluminum back. You end up with two flat, parallel surfaces front and back that give the phone its precision, camera-like feel. It also makes it possible to make simple tripod mounts and to use the phone as a camera on flat surfaces.
I don't think they'll ever return to the slippery shape of the 3G/3GS, where Samsung is stuck, notice.