AirNZ have half the 737 fleet and all A320's fitted with RNP Navigation equipment that allows them to operate to minima's well below non-RNP aircraft.
Air NZ's current RNP is 0.11 (req nav performance within 0.11Nm of track)
Jetstar are currently doing "proving" flights to get their RNP qualification. I believe they have an interim approval to RNP 0.3 which still only allows them to the same minima as the VOR/DME approaches. Proving flights incl as much as 300+ approaches in weather better or equal to the VOR/DME minima.
PacBlu's B738's are RNP capable but they are not attempting RNP approval with CAA so they'll be restricted to the VOR/DME minima.
So in answer to your question, AirNZ is the only player because they're the only ones to have completed RNP certification.
S2K