I dont know anything about the incident in Cairns nor much about Cairns approach in general - so it would be inappropriate for me to comment on the specifics. (do you hear me dick?)
However speaking in general terms I will say that sequencing lighties in with Jets and high performance turboprops is not always an easy thing to do. A C172 gets swallowed by a 767 at a truly alarming rate.
Sequencing is an art - even very competent controllers with many years experience still get it wrong occasionally. It never ceases to amaze me how willing many pilots are to second guess ATC decisions on sequencing. It is also incredible the conspiracy theories that abound about favourable treatment of one subset of industry or another by ATC. The fact is that there is generally very little latitude for ATC to favour one aircraft over another. The sequence is arranged to get the aircraft over the threshold at the agreed rate as efficiently as possible - I have never in my career seen or heard of any policy of conscious favouratism being applied to any airline.
As part of my training we studied an NTSB report detailing the results of getting it wrong sequencing jets behind a C172. I believe it took place at O'Hare in the early 90s. On this occasion the ATC chose not to pull the cessna out and wound up with a serious traffic jam behind him - and subsequently put on an airshow over Chicago trying to sort out the resulting mess- some of the planes got VERY close indeed. The report should be available from the NTSB database, I recommend it as required reading before suggesting you know better than the guy doing the vectoring.