To respond to your last question first, NO the rules haven’t changed, it’s just that your Owners Corporation hasn’t been following them.
The “rules”, specifically Schedule 2 Clause 34 of the NSW Strata Schemes Management Act (1996), states that compulsory Motions on the Agenda for Annual General Meetings (AGM) MUST include one for the Owners Corporation (O/C) to elect the Members of its Executive Committee (E/C) and to decide the number of those – which may not exceed nine(9).
The positions of Chairman, Secretary, and Treasurer are then decided on the basis of a vote by the elected Members, usually at an E/C Meeting convened immediately after the AGM, and it’s then that any nominations (including self-nominations) may be voted down if that’s the majority view of those in attendance.
In circumstances such as those at your Plan where it appears that an active E/C is not desired by a majority of Owners, then the functions (but not the positions) of Chairman, Secretary, and Treasurer may be delegated to your Strata Manager, but only under a term of a Strata Management Agency Agreement that they’re required to hold with the O/C.