Your thoughts are very close but not identical to the NSW Fencing Act, which according to the “Who’s responsible?” document, basically says:
If a fence …
1. Divides two lots. Each owner is responsible 50/50
2. Divides one lot from common property. The owner is responsible 50% & the owners corporation is responsible 50%
3. Divides one lot from the adjoining property [which is not part of the strata scheme]. The owners corporation are responsible for 100% of its share.
In the absence of specific legislation or guidelines, I would use the above until someone told you you couldn’t.