"In Webster v Mercury Colleges Pty Ltd, Fair Work Australia held that
termination of a sponsored teacher was unfair because of the serious financial
consequences to the teacher and the social dislocation that was inevitable as a
result his summary dismissal."
Webster v Mercury Colleges Pty Ltd was a case of wrongful dismissal for gross misconduct.
Whilst the above quote is true the ruling by FWA was not purely based on the issue of the visa, it was also ruled on with consideration of the employer not following due process and the employee not given procedural fairness in the dismissal. The outcome was too harsh. Basically the punishment outweighed the crime in such that the punishment would have resulted in the employee, due to the terms of his visa, being required to return to his homeland and would have caused "harsh" financial consequences far beyond that of a citizen of Australia.
On the flip side this case also puts a more onerous burden on an employer. Employers maybe more prone to hire a local worker than a V 457ener in the future as it potentially could be harder to dismiss the fly ins in the case of any misconduct.
In regard to preferential treatment given to 457eners, my opinion is an employer cannot discriminate when determining a reduction in staff in a work force. An employer on a 457 visa will be subject to the same conditions of employment and the same due process as a local employee subject to the conditions of their contract/award.