mini I'm relatively sure that's not the case. That method is used in Medicine but not elsewhere, as far as I know. As Melbourne sees it, a 'weighted average' refers to:
'The grade weighted average weights subjects to reflect their credit point value. This is calculated by multiplying the mark received for each subject against that subject's credit point value. Each multiplication is then added together and then divided by the total amount of credit points for subjects undertaken.'
The term is just used to ensure that say, Biomed HSF, is weighted more heavily than a 'normal' 12.5 subject because it's worth double the points.
All years will be counted equally under this scheme.
You're welcome to enquire though?
Also keep in mind OP that just because the minimum is 65 does not guarantee you a place in Honours. In my department the official minimum is 65 but the department sets a minimum of 75.
Edit: here is a backup from the official policy:
'c) The SGPA will be calculated as a credit-point weighted average of the remaining 275 points.' which reiterates what I said before.
Source:
https://policy.unimelb.edu.au/MPF1053