Actually I thought the same way at the beginning. The problem when doing a "moving forward" system, is that you have to rotate the camera. In fact, if you dont, when you move towards the camera, your inputs are the other way round, because it's on the player's (the object) referential.
But I didn't want to have a rotating camera, so I had no choice but to use this type of input.
I hope this was clear enough ^^