It is different in Victoria.
For a start a “unit” often means a villa house – not an apartment.
The OP’s strata seems typical of older strata plans in Victoria where the plan number begins with RP or SP. In those type of horizontal strata plans the lots typically own the land below and airspace above their lot to a certain distance (eg four feet or one metre). And lot boundaries are typically “median” which means they are 50/50 with another lot or 50/50 with common property.
It can make the cost sharing of boundary wall maintenance “interesting”.
One way, if the OC passes a Special Resolution, is for the OC to decide to pay for all of the works regardless of if it’s to lot or to common property. That can make logical and even financial sense. But it does need a Special Resolution to approve it.