Holden Barina 2009: Front brakes need machining?

Brakes are regarded as consumable items, which are not covered by the warranty. The warranty is there to address defective items in the car. You could argue that a vibration in the brakes must mean there's a defect in them, but the time and effort required to prove that the   vibration was due to a defective part and not use or abuse would be too much to justify doing it.