I disagree and think it's ignorant to believe that motivation has no relevance at all. Of course motivation is relevant. If an airline can argue their motivations were completely innocent and out of their control, then they are less liable for compensation to affected passengers. .... then the motivation for that decision is EXTREMELY relevant and to suggest otherwise is almost unbelieveably immature and ignorant..
It may be a matter of terminology .... but really there are only two reasons for delays. Those within the control of the airline (all of these are most definitely "operational reasons") , and those that are beyond the airlines control (sometimes often called "operational reasons", but usually airlines will blame something if they can and avoid using such a vague term, so will blame weather/air traffic control etc if they can).
For the first set which are within the airlines control, I stand by my position that SPECIFIC motivation for this type of delay/cancellation is irrelevant, especially if it is just speculation (albeit well-informed speculation). Whether it is commercial re-scheduling due to light loads, lack of crew availability, mechanical issues, aircraft late out of servicing - it doesn't really matter. It is an airline caused delay and you have a claim irrespective of what type of delay has caused it. Keep it simple, and avoid the speculation in correspondence (but it's OK to speculate here on AFF of course). Think of the person reading your claim. If you want to complain about this practice of last minute cancellations, complain, but in a different complaint from your financial claim.
With other delays (outside the airlines control, such as weather related delays) then airlines usually will do everything possible they can to avoid being liable for meal/accommodation etc. Although to be fair to QF they do cop these sorts of delays on the chin and usually try to assist passengers. In some parts of the world, you will get nothing, even for delays caused by bird strikes (out of their control).
Clearly, Qantas have accepted liability by providing accommodation, so it seems prima facie your claim is justifiable. However, if you resubmitted your claim on June 12 to meet their requirement, the way the corporate world works these days, I would be more surprised if they had paid out within a week, than if they hadn't.