Based on comments from Ken Callender when he hosted the 2KY sanitised talk-back:

Apparently it is a massive undertaking to change the rail at Randwick. After which the track is re-surveyed and starting positions changed so that the distances are precise.

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However some tracks apparently leave the barriers unchanged and instead alter the distance.

For example I note that Cheltenham recently had distances of 2250, 2265 and 2271.