The Dying Art of Customer Service

I ordered a birthday gift for my sister from a website I order from frequently. The gift card instruction box gave me pause at the time – instead of the usual "check here if this is a gift" type thing, the site had a weird instruction to "note that it’s a gift in the comments box." It was totally unclear how you included a gift message, but I decided to type that in the comments box, too, and hope for the best. (I felt rather like my grandfather, who always spoke to answering machines as if they were secretaries. "Please ask Debra to give me a call," I would hear when I played messages.) Today, I heard from my sister that she got a great gift with no card or indication of who sent it. Luckily, she guessed it was me. I emailed the website to complain and got (very promptly, which was nice) an apology along with a statement that the card WAS included and the recipient no doubt overlooked it. Basically, the response was "Sorry, but we’re right and your gift recipient is wrong." How is it possible for anyone not to get that the explanation totally undercuts the apology and makes this a bad response? Even if it were true, where's the corporate upside in telling me my sister is wrong? And what ever happened to "the customer is always right?" It would have been fine with me if the apologizer had typed "I’m sorry you were disappointed. We make every effort to assure that cards get included, but sometimes, blah, blah, blah," then hit send, and called me something unflattering to the person in the next cubicle. I don't expect groveling, but it seems to me that businesses might seek customer service reps who understand that corrective rebuttal is probably not the most effective approach to customers.