The reasoning as I remember it related to being an air force airport, in constructing the new M! there was a height restriction and basically not allowed to either move or raise the existing power lines/power grid. Don't know how many or what sort of low level runs they do in that area for that to be a design/construction factor. I guess a power line at that speed might be a bit harder to spot from the cockpit for their pilots.
Where the intended change to existing infrastructure is, in any sort of proximity, is about 8Km east, when using the westerly approach. They actually approach from further north (over the dam), to avoid flying over Raymond Terrace. The bit that is to be upgraded, is from just before Hexham Bridge, to the northern edge of Raymond Terrace. And the only deviation from the existing road/highway is a small swing around the southern edge of the Heatherbrae industrial area, which is in the 45M height restriction area.
So really can't see any problem with that.