Payload Comparision
One thing to take into account when comparing the Max payloads of the B777 and the A380 is that the A380 has a small cargo hold compared with it's cabin space. On long routes the cargo hold will be mostly full with Pax baggage - there is little space left for freight - therefore less need for higher MZFW. For an a/c carrying ~500Pax and with not much space for heavy cargo a Max Payload of 66t (taking the high OEW's resulting from airlines choices) sounds more then adequate.