People love the original beauty of iPhone 4, want to show the logo and colour of the device, but still decorate and protect them. Cases in transparent or with holes at the back are usually preferable. Since they love their iPhone, sufficient protection is wanted and hard cases are usually the choices.
See the Whole Back:
Rim Series Hard iPhone 4 Case
Perla Series Hard iPhone 4 Cases
S-Line Series iPhone 4 Silicone Cases