I believe that the T&C's say that the Melbourne Cup cruises they were offering the alternative of Onboard Spending Money. It is common (understandably) to not include drinks packages to cruises that are linked to a lot of boozing (ie Melb Cup, State of Origin etc).
"Onboard Spending Money is per room in AUD and applies to cruises 6 nights or less and the 7 and 8 night Melbourne Cup sailings –i250, i350, v359, v247).