the reason you dont need to have a switch to power the camera, is because you should have the camera powered up anytime the radio is on. this way you can just select rear view anytime you want no matter if you going forward or not.
too many people power the camera up directly from the reverse lights of the car, and this would cause the camera to only be powered up when the reverse lights are on(only when the car is in reverse) this can also have two big problems depending on the car, 1) if the car has a computer that tells you when the light bulbs are out, the camera could trick the computer to either tell you that the bulb is out when it is not, or not tell you the the bulb is burnt out when it actually is. 2) if the car has factory LED reverse bulbs, the car might not have enough current to power up the camera and the reverse bulbs and you could burn up a circuit in the car (probably not too likely but it is possible)
all camera are the same in how they work, there is a signal cable and power cables, you just need to have the camera powered up the right way for everything to function correctly.