Wrong decision making.
Why did the pilot allow himself to get into to a situation where he lost control of his aeroplane, there is evidence to suggest that he was concerned about the weather conditions, why did he elect to continue on? These are the questions that we as a pilot group/industry must be asking, and reflect on our own experiences. Forget the ATSB and CASA they will just do what they normally do. Who cares about ailerons being here there and everywhere and temperatures and ground speeds - we know all that. The aircraft should never have been put into an out of control situation.
CFIT, VMC into IMC, overloading aircraft, operating aircraft with known un-servicabilities that render it un-airworthy, busting CTA and the list goes on and on. The crux of the issue is pilot discipline. Sadly flight standards have significantly dropped right throughout the entire pilot group IMHO. We can point our fingers at regulators, governments and a myriad of other organisations and individuals, however we as individuals are always accountable for our own personal discipline.