WTF? - if I flight plan to an airport and look up the current actual QNH then I can reduce the alternate minima by 1000 feet? I plan alternate minima based on runway I might be using? Who writes this crap?
No. Only 100 feet.
I think what a lot of people who write these reports, and many who comment on the reports don't have is an understanding of the mental processes going on real time for the crews when a situation like this is unfolding. It is fine and dandy to sit at a desk and flick through the regs to confirm that the crew should have technically made diversion decisions based on the TAF not on the observation.
It is a completely different thing to be doing 450kts across the ground using two tonne an hour and realising that the forecasts you based your fuel load on have been wrong and that your Plan A is not going to happen. When developing plan B information is gathered and options considered. Both crews were presented with information ( the Mildura met observation) that suggested a safe landing could be made at Mildura. At this point in time, when 'the system' is not working as advertised, real likely outcomes are more important to the crew than regulations. So they should be too, the crew have to make whatever decisions are necessary to keep their aircraft safe.
If this situation was presented to a new Captain in a simulator as a LOFT and the new Captain decided that holding in the hope that the unforecast fog cleared was a more appropriate decision than diverting to a field nearby that was reported as being open, many check Captains would debrief that as a new Captain, don't forget your primary role is to keep the aircraft safe and if you have to break the regs to do that,my then so be it.