Actually, even names can have problems. getLastName(), for example, isn't culturally universal. In many Arabic countries, what we would think of as a "last name" is actually the father's name. More over, the same person can be identified in more than one way (roughly translated as "father of" and "son of"). Two different "last names" can identify the same person! Exposing a "last name," then, could cause problems when you try to move your application to a country that uses these naming conventions. Even comparison becomes difficult becuase you have to determine that two seemingly different names actually identify the same person!

Admitedly, this is all probably hair splitting for you average shopping-cart application. My point is that the side effects of exposing any implemenation details can be unobvious.