My understanding is that NBN only cables to an access point at or near the individualunits (although I may be wrong in this case). [Turns out I was – see Bubbles post below].
Then it is up to the service provider (like Telstra or IINET) to connect the modems inside the lots. This is a reasonable upgrade if the majority of owners agree. If they don’t they can vote to prevent it. But there is a principle here of collective responsibility taking precedence over individual choice. I don’t swim but I contribute my share of the levies for the heating and upkeep of the pool.
To many people, upgrading to NBN is as fundamental in a modern building as installing a TV aerial that receives digital signals. You might not want it or need it but, given that NBN have said “all or nothing” then you have to console yourself with the thought that you might change your mind or future owners will be glad that it’s there as an option.