Technically , you CAN create full Nandroid backup without rooting the device .

Technically, you CAN create full Nandroid backup without rooting the device. You just need to flash CWM (or, any recovery which supports Nandroid backup) over USB. For example, you can use Odin (Windows) to flash CWM to Samsung devices after going to download mode, all without touching the Android. So, there's no rooting or root access involved at all.