Good question 'loc' and one that should be answered promptly by Flight Ops. "Is diverting cheaper than a few tons more?"
A company cannot have a 'fuel policy' based around a few trite words in the FCom and some changes to the Flight Plan. Otherwise pilots will continue to carry 'a few tons more'.
Just consider the cost of carrying a 'few tons more' particularly on QR long range flights every day. Not just in monetary terms but also in wastage of resources?
A professional operation means carrying fuel when considered necessary with the airline accepting the odd diversion will happen if the forecast is wrong.
GB
(You might just care to check regarding being paid for diversions. I was told we do? Whether that's true and/or how the pay is calculated, I don't know?)