clotted, I'd be loathe to say your friends are lying. Much more likely, they misunderstand the Qantas system and its nuances. This is common.
"MDC" is a thing called "Minimum Daily Credit". This is something which was primarily pushed by the pilots to make flying patterns more efficient. The aim, with the full support of pilots, was to encourage planners to not have them flying down to melbourne, sit around for 6 hours, fly back to sydney, and get 2 hours pay for an entire day away from home. Rather, they would get 5 hours 30 minutes pay per calendar day away, and Management could then do with them as they please. This suited the pilots, and it suited the managers, and it was strongly pressed home in negotiations by those "rogues" in the pilots union, AIPA.
One in-built protection is that if the flying hours exceeds 5:30 per day (as it often does), then you get paid a little extra directly proportional to those extra hours. However the catch is that we are paid at a lower hourly rate than the guys who are specifically paid by the flying hour.
If I do 10 hours duty during the day, or 10 hours duty during the night with toothpicks propping open my eyelids, it doesn't matter a fig. If I do back-of-clock flying, doesn't matter. More duty hours due to delays etc? Doesn't matter. No extra pay for me (with the exception of unplanned extensions above the normal CASA limits, as permitted at the pilots discretion by CARs). I am honestly at a loss to explain what more Alan Joyce wants from me, unless he wants to change Civil Aviation Regulations to allow far more flying hours to be flown or much longer tours of duty. Of course, Alan knows he can't do this. But he also knows that if you base your airline crews in an Asian country, you're generally unhindered by such ancient dinosaur western work practice concerns based around outdated principles like fatigue management, risk assessment, & so on.
Much like some company execs who appear quite happy to have their running shoes made by a 12 year old working a 15 hour shift for $0.30/hr in a factory somewhere north of Manila. Similar principle and mentality.