From FAR 23:
(4) The takeoff safety speed, V2, in terms of calibrated airspeed, must be selected by the applicant so as to allow the gradient of climb required in §23.67 (c)(1) and (c)(2) but must not be less than 1.10 VMC or less than 1.20 VS1.
so definitely not a unique Australian term but perhaps the old Department thought that it was a more meaningful set of words to use in their standardised AFMs rather than V2 or whatever.
Apart from the climb requirements referenced in that paragraph there are one-engine inoperative performance requirements as appropriate. I'm sure that others can give examples of where they need to be able to get the climb performance provided in the AFM and that is only achievable at the right speeds.
Operating a 300 hp Pitts in the Rocky Mountains I didn't need to know Vx or Vy, I'd just point the nose over the mountain and we'd get over it. Different thing in a heavily loaded 172 taking off at 8,000 density altitude - not much rate of climb at Vy. Not going anywhere useful at any slightly higher speed.