After reading the DPI document it seems as though jet competition is only unrestrained to the major ports and routes listed, this is services between Perth and Kalgoorlie, Port Hedland, Karratha and Broome.
The document is very long winded but i could not find any reference to jet/turboprop bias.
Geraldton only just crossed the threshold of 55000 (2003-04') pax per year to allow limited, staged competition. There is nothing stating whether the competition is jet or not, there is a tender process and an operator is granted exclusive rights (props, jets or whetever). Currently the system is under review with the two main regions to expire in december, it was reviewed in 2003-04 and decided to continue with periodic reviews.
Being tender based with an emphasis on sustainable air services it would be understandable that the ports look as if they are turboprop only but maybe thats because props offer the lowest operational cost per seat.