I think you'll find that VFR pilot flew into the sea in Vic due to turning out to sea in low vis conditions and lost total reference to a visual horizon. As a VFR pilot he unfortunately probably didn't have a scan rate quick enough to pick up the descent at low level prior to impacting the water.
Pyro - you don't "set" a VSI and even if a static vent was blocket the AH will show an attitude change away from S&L - as will the ASI and in the case of that accident the DI as the aircraft made a right turn out to sea.
Even though VFR pilots are given training in Instrument flying as part of the GFPT it would be foolish to rely on that very limited experience to enter IFR conditions.