Just had my 2013 XTS in for the first service. All is well but while there, I trolled the showroom and noticed that the 2013 XTS and ATS on the floor had different grills, headlights, and taillights but still listed as 2013 models.
I'd bet your dealer has a couple of specials with aftermarket replacements that they are trying to sell at an upcharge.
Last time I had my car in for service, they had an XTS on the floor with a custom grill and wheels. It was not an improvement.