It all depends on the routing rules. For MEL/OOL connections via SYD are generally listed.
You will find that for MEL/SYD the rules would show something like "direct flight only".
Going back 10-20 years you could often connect on high value fares through Canberra but this was tightened up in the latter part of the last decade.
Here are some routing rules for MEL-OOL on VA:
Results from ExpertFlyer.com
Code:
Fare Routing Search:
Departing MEL on 15/07/14 for OOL
Fare basis code SZDA
Flying VA
Routing via Eastern Hemisphere
MEL-OOL CXR-VA TUE 15JUL14 USD
THE FOLLOWING CARRIERS ALSO PUBLISH FARES MEL-OOL:
DJ EK EY JQ QF U0
**AUSTRALIAN GST INCLUDED IN BASE FARE**
//SEE FQHELP FOR INFORMATION ABOUT THE NEW FARE DISPLAYS//
SURCHARGE FOR PAPER TICKET MAY BE ADDED WHEN ITIN PRICED
AUD CONVERTED TO USD USING BSR 1 USD - 1.0669 AUD
V FARE BASIS BK FARE TRAVEL-TICKET AP MINMAX RTG
1 SZDA S‡X 76.00 D28MR T31JL -/‡ -/ - 1
2 SZDA S‡X 85.00 ---- -/‡ -/ - 1
3 SZDA S‡X 90.00 ---- -/‡ -/ - 9000
*** THERE ARE NO YY REQUESTED FARES PUBLISHED MEL-OOL ***
1* TRAVEL MUST BE DIRECT
9000* 1. MEL-ADL/CBR/SYD-OOL
TRAVEL MUST NOT BE NONSTOP
.