Just on the Sydney Airport line....The Politicians may love it, but you can bet that apart from a 'photo opportunity' none of then would use it when they needed to go to the Airport, be it for a 'business trip (aka junket)' or a holiday.
Don't necessarily believe everything you think...
Minister Allan was on ABC radio this afternoon describing her use of the Sydney Airport line...
When it was opened in 2000 I was sceptical (the Government operated buses which were cheap and frequent), and apart from the Surcharge that results in the present Adult fare of $18.50 for the 2 Airport stations it works well as it feeds straight into the City Circle and has integrated well with the East Hills line (and the Illawarra Line via a change at Wolli Creek). For a day tripper, or someone with light luggage, it sure beats the $40 - $50 Taxi Fare into the CBD and even if you have to stand its only for 10-15 minutes which is faster than by road.
But if you are lugging a 25kg suitcase its not so good, as you are then restricted to the vestibule ends of the double deck carriages, and the lifts at Central (no escalators to the Airport platforms at Central) and the other CBD stations to get you to platform level are small and you may find quite a lineup waiting - avoid the peak hours at all costs.
There is an active freight line (to Cooks River and Port Botany) on the north side of Sydney airport, but coming in via that would have needed a lot of work at Sydenham, not to mention a fork to get to the two terminals - and would have resulted in a dead end line rather than the through line it has. No trains terminate at the Airport, all are normal suburban sets that travel beyond as far as Macarthur.