A castellan is 170 usd (about 238 aud) vs actual price of 280 aud. Given that the average wage here is higher, that theory doesn't appear to hold much water.
Is lvo itc rules? Was cancon itc? Were players building lists appropriate for the mission pack and that's the difference?
Edit: IK were already popular here with many players already having a knight or 5,while I understand that it wasn't quite as common in 'murica, so there could be an aspect of pragmatism in it.