Its not all that simple as other things are having an influence, such as..
Why do the registration rules for vessels differ from those of vehicles?
www.rms.nsw.gov.au/roads/registration/get-nsw-registration/index.html General requirements in Australian jurisdictions
The common view in Australian states and territories is that any vehicle should be registered in the state or territory in which the owner/operator lives and where the vehicle is generally kept.Where you are a genuine visitor, or temporarily in NSW, and you drive a vehicle that is registered in your home state on NSW roads, you will not require NSW registration.
Visiting overseas vehicles
Vehicles that are registered overseas and only in NSW temporarily do not require NSW registration, as long as all plates and labels required by the overseas registration authority are displayed. Roads and Maritime also recommends that the overseas Certificate of Registration is carried when using the vehicle.
Yet NSW requires visiting vessels to be registered, why the difference? Interstate and overseas vesselsYou can use a vessel registered in another Australian state or territory, or overseas, on NSW navigable waters. If you're using the vessel temporarily in NSW, you don't need to get NSW registration, as long as the vessel:
Is not ordinarily used on navigable waters in NSW
Has not been in NSW for more than three months Is currently registered in another state, territory or overseas
Is properly numbered and carries an identification plate required by the law of its home state, territory or country.
If any of these conditions cannot be met, and the vessel is registrable under NSW law, it must carry NSW registration when on navigable waters in NSW. If the home state, territory or overseas country does not have a vessel registration requirement, the vessel must be registered in NSW, or another state.
A notice issued to Visiting and Transiting Vessels also state that after 90 days not only is NSW Registration require but that vessel also requires, quote "a Marina Berth, Legal Wet Berth or Mooring License issued by the RMS.
And then there is the 'RMS perceived' problem of the
quote "Hundreds" of liveaboards in NSW. I have heard of a whisper that the Lake is about to be "cleaned out". Our problem is that the RMS don't see us [day sailors and cruisers] as a problem. I've been told that a warning will always be issued first as the RMS is not up to losing when fines are challenged in court, seems they don't have the money for court cases they may loose.
I also think mooring minders are in there as well.