The tyres/brakes thing could be a red herring.
Several airlines (indeed most that I have dealt with in the UK) have differing criteria for tyre/brake removal at home base rather than outstation.
The criteria for outstation is the approved limit (e.g. worn to base of groove), with the criteria for home base being slightly less (e.g. for tyres it might be 1mm groove depth and under)
This is to ensure that there is enough rubber/carbon to last the day's operation, so that wheel/tyre changes (= delays) are greatly reduced during the day, and the logistics are better as there is less to ship back from outstations.
A well run outfit will have varying criteria for outstation/home base for such items with a soft limit for home base and a hard limit (approved minima) for outstations. This saves money for the airline, making best use of materiel and manpower, but without affecting safety/airworthiness.
The amber zone/red zone philosophy is something that 'good' airlines use.
To the uninitiated, it would look suspicious (bulk of servicing/component changes conveniently done at home).
The anology would be topping up the oil/water on your car at the start of a trip before it hits the low level mark, rather than just waiting for the red warning light to come on the dashboard.