Different carriers have different redemption rates, even within the Star Alliance.
Begging to differ with fly747first-- on UA, the 120,000 mile first class ticket to Australia or New Zealand is available on UA or NZ metal. Same for the 90,000 business class ticket. My wife and I flew ORD-SFO-AKL / CHC-LAX-ORD in business class for 90K UA miles each. It was a great deal, and a great trip.
Every airline has its quirk within the *A. Australia/NZ happens to be the quirk in the UA scheme.