I read a thesis a few years ago examining the feasibility of flying LHR - SYD non stop which included some Jeppeson flight plans. The shortest route in each direction varied considerably by season - it could mean overflying HKG or Tokyo. Obviously winds vary day by day ,not just by season, and changes can make quite different routings the most economic. Also, I don't know if it is the case here but overflying rights and costs can result in different routes being taken.