I have to say, I can't think of a single good reason for this couple to have gone to the press about this.
If I were in the waitress' shoes, I would have found the card offensive also. While it's possible that the couple gives the card to everyone, it does seem more likely that they gave it to her specifically because she is pregnant. It's akin to saying, "We can do better for your baby than you can, so please consider giving him to us."
However, it wouldn't have crossed my mind to go to the press with it. I would have expressed my disgust by throwing the card out and venting to my husband.