What is so special about a camera on an iPod? I don't know, maybe its just me.
There wouldn't be anything special about a camera on a nano or a classic. It would just be a gimmick.
On the touch, the camera can be used in conjunction with several apps that are only currently available for iPhone users. Also, there are a bunch of cool camera effect Apps like ToyCamera, OldCamera, CameraBag, Pano, etc.