When I was in customer service I used to investigate and respond to complaints (this was for the airport authority) and usually many people were happy with an explanation and an apology. This just shows that the previous comments on this thread are totally accurate, everyone is used to a standard letter these days.
Of course if the complaint was just something, for example about ground connections or a delay, I had standard letters ready too
I wrote to an airline about an issue I had in January, got a standard letter saying that they would deal with it within six weeks, still no response in August, would I fly with them again? Well yes being a member of their FF club and them being cheap and convenient on a route I fly often. Not happy with myself but that's what they do!
XSB