Firewall - what you say is spot on but in my opinion any Captain worth his pay should be able to anticipate a tailwind with the curfew, or at worst have the common sense to carry a few extra tonnes of fuel (lets call it 6 tonnes to carry the 5 odd tonnes for 30 holding and a bit extra burn to carry it) especially with the curfew limitations of using 34L between 0530-0600.
15 kts TW on a B744 isnt alot lets face it.
SIN-SYD shouldnt be limiting fuel wise but SQ seems very adverse to crew carrying extra fuel - anywhere.
The gentleman Captain for a particular asian carrier being escorted by police (supposedly under arrest for landing with 1600kg total fuel in a 747-400 at LHR) from the a particular hotel in Kensington London should be used as a pin-up boy for fuel management courses.
Unfortunately with the advent of accurate flight plans and pressure from bean-counters alot of crews seem hesitant in taking any extra fuel and seem to using less of the experience gained over the years anticipating unforecasted weather at the destination requiring additionall fuel or an alternate which a computer just cant do.