Well, one of the reasons. I recently had two issues with iTunes. I purchased a season of Scooby Doo (for the kids of course) on my AppleTV, but only 3 of the 8 episodes downloaded for some reason. I reported a problem with my purchase, and within 4 hours or so, I had a response with some troubleshooting ideas. They didn't work. Without a hassle, they reinstated the 5 missing episodes and I was able to download. Great customer service.
I have been listening to 3 purchased albums from a very cool band, Ike, recently. Unfortunately, on one of the two albums, three of the songs have a blip in the middle of the track. Very annoying. I again contacted iTunes and without question or hassle issued 3 download credits and asked that I wait three weeks so they could investigate. Awesome customer service.