As mentioned further up (sorry, not trawling back to find the post to quote it), Consumer Protection law precludes reliance on unfair Terms and Conditions, where conditions were imposed unilaterally, and the consumer had no means to negotiate.
What would be deemed unfair would depend on all the circumstances. The terms being repeatedly quoted and relies upon about a confirmed booking not guaranteeing performance with respect to time or date, or cabin need to be considered in the actual circumstances. Where the inabiltiy of the airline to perform is beyond its control - such as weather delays, acts of god, or unexpected equipment failure, reliance on these terms, and their presence may be deemed reasonable. (Take note that under the European regulations, equipment failure due to insufficient maintenance etc is not considered outside the control of the airline). In these circumstances, the airline may be deemed to not be in breach of the contract, and following there procedures (i.e. accepting what is offered). In the case where the airline offers carriage in the booked cabin at a later date, and pays for the accommodation, and the passenger chooses to travel earlier with a downgrade, there may not be much leverage to demand compensation other than what the airline is willing to offer.
However, if the failure is caused by something directly within the airlines control - such as overbooking, the terms may be viewed very differently. Those terms that let an airline bump a passenger at will with impunity may be viewed as unenforceable, leaving the airline libable for damages for breach of contract. In that situation, the damages recoverable may not be restricted just to direct loss, but may include consquential damages. If the passenge in mitigation were to book an alternative ticket in the same class of carriage on another carrier, then the cost should be recoverable directly as damages arising from breach of contract (although in that case, you would not expect to recover a refund of the original fare). Should costs be incurred due to delay - such as having to reschedule appointments, this may well be recoverable as well. Given the situation being discussed here, where the pax had a confirmed booking on a flight, and that flight departed with the scheduled equipment, there is no way for the airline to dispute that the breach of contract was something that was solely within the control of the airline, and thus something they should be prime facie liable for.
The distinction between the two situation is also (as well as other reasons) highly likely to be a factor into why, when a cancellation does occur, passengers are not generally bumped off other flights to make room for the affected passengers, but those passengers can be delayed for much longer waiting for availabiltiy. Bumping someone from a flight by choice would expose the airline to damages for breach, as they know that the Terms and Conditions are of dubious enforceabiltiy, but they are on much safer ground where a force majuere event has affected a flight.
None of the above should be taken as advice. I would suggest that the affected pax may be surprised at what may change as far as offered compensation should QF be approched by either Consumer Affairs or a lawyer acting on their behalf. There are have been many anecdotes about airlines customer relations blustering behind the T&C and attempting to bluff, only for the legal department to be in a great hurry to settle once it becomes obvious that someone is serious about having their rights enforced in a court.
Well said. My summary is that there is a big difference between getting bumped due to a force majeure event, or even due to mechanical/technical issues vs. overbooking. Force majeure = Less compensation or none at all (just put on the next flight available) because cough happens (and just hope your travel insurance will cover it). Over booking = they are completely at fault and you should expect to be compensated.