Because you may have different settings (the SHIFT-A settings) on your FZ5 than someone else, or be using different samples for gear whine, or blow off, or combustion sample or whathave you.
edit: or are you alluding to the fact that the engines are "supposed to be the same", so they shouldn't be allowed to sound different? If that's what you meant then... I guess you're right.... Although some folks would like BOVs to be transferred at least, that's the only real circumstance I could think of TBH. Good point.