probably has something to do with the fees of processing, the contracts these betting establishments have with the different money establishments, and the amount and efficiency people that handling and overseeing the operations.
SIA probably waits 2 days to give them a chance to catch up and/or to dodge some fees. SIA has gotten my withdrawal to my neteller always between 1 to 2 days.
any other possibilities?
Pinnacle is an internet only operation i know that might have something to do with the efficiency of their operation.