I understand that people may accidentally cover or touch the camera lens. However, regardless of where the camera is, people will adjust their grip when then look on the screen and realise that their finger is covering it. Regardless of where the camera is, people may accidently touch it during everyday use. When I need to take a picture, I just wipe the lense just in case.
I think the positioning of the camera may be due to how the internal components are arranged. Being off centred is not going to be an issue except for perhaps macro shots. For normal distance shots, being off centred by a few inches is not going to affect the overall angle of the shot. For macro shots, you just have to check the location of the camera and then move the phone a few inches to ensure your shot is shooting the subject at the correct angle.