Late Developer
Fog can clear very quickly once the temperature starts to pick up. The fire engine could have been there for any number of reasons.
I don't believe that VS take any less fuel than any other long haul operator. As has been said by many experienced pilots on this thread already, the best laid plans of mice and men sometimes go wrong and a diversion can become necessary.
I think I'd rather rely on the flight crews judgement of how much fuel to take, rather than listening to demands from the back.