To be fair, events of this size, tours of this size, would always book in Plan B's at the same time as they book in Plan A's. There is a lot riding on these things, and you want to be able to put forward Plan B as soon as possible so as to limit issues or disappointment. Remember that this week a hurricane could have whipped through Auckland and ripped part of the stadium apart, or the cargo plane could have overshot the runway landing in Sydney and rendered the stage useless, or a million other things and caused a similar postponement. These things are planned for.
As it stands these concerts have been originally scheduled to take place in the final weeks just before the football season starts here in Australia, which knocks these stadiums out until mid September. Word is late September/early October are the new scheduled dates, and I'd suggest those have been locked in 'just in case' all along. It would be poor planning if they weren't, remembering as I said, any number of hundreds of things can and could cause such a postponement at very short notice.