There can be little doubt that CASA have "pet" operators and projects, and you need to look no further than the grounding of Tiger Airlines for their descent below MDA on approach to YMAV.
Have a trawl through the ATSB weekly summaries
ATSB link and sooner or later you'll find an incident with an RPT jet that would be equally as life threatening and deserving of similar sanctions. While not identified, they can't all be Tiger (i.e. QF,
VB etc).
Another already mentioned here is the determination to bust Quadrio, the cost of which would have been significant. Had that same diligence and determination been directed at Hempel he would have been grounded years ago.
Another thing - I don't believe the discussion (while enlightening) about AOC and Warbirds addresses the root cause of the accident. Hempel was well known to CASA and there is no doubt they were aware of his capacity to ignore the rules.
Put simply, CASA chose to smack him with a feather when they could have wielded a big stick up to and including a custodial sentence. Had they enforced the regulations as they are duty bound to do, this tragedy would not have happened. There is a earlier mention of 7 FOI's in Brisbane - it would only need one of them to sort him out. Go figure!