I too have written emails to United Airlines about my travels. I write both positive and negative stuff. So far I have cashed in $1300 and 20000 points!
When I wrote to SAS I got either the "sorry, blah,blah,blah" reply or not even one at all.
And why this is.....well.....I`ll keep my mouth shut as I don`t want/ or not permitted to say the real reason for it!