The op wasn't about B75/76 but one of the reasons you can use centre tank fuel on these aircraft is that all the fuel pumps are operating all the time. The centre tank pumps operate at a higher pressure than the wing tank pumps and thus the aircraft uses centre tank fuel first. If the centre tank pumps fail, the wing tank pumps are already operating and can provide a continuas flow in a very high power and critical situation, without the engine being starved by low pressure. This is not the case in the A320. In this aircraft a low fuel pressure would have to be sensed before the aircraft would switch to wing tank fuel.