For what it is worth, my better half and I were on a QF flight out of Darwin for Brisbane on the usual el cheapo ticket, in May this year, and the inflight entertainment system failed to start. No great problem, had a good book to read, and thought no more of it.
Some weeks later a voucher from QF for $150 arrived in the mail, with an apology. We were stunned and amazed, and very appreciative.
Does this happen very often?