Does anyone know why some airlines' tickets have long durations (eg 12 months on QANTAS) and others have short durations (eg 14 days on SQ) with others in between (eg 3-4 months on EK). These are even for their discount fares (I know they all have 12 month tickets, but with SQ and EK, they are normally full price fares). I book return flights out of Asia which means the only airline I fly with now is QF. I am curious however on how and why their model differs from QF.