1 Warren Wise, December 9, 2012 at 5:21 p.m.:

The explanation of why getter methods are needed is incorrect. Returning a mutable object in a method definition will still create an alias. In the case of a list, you'd have to return a copy of the list in order to prevent aliasing. The getter method enables you to return a copy (which the instructor did not do in her implementation).

Additionally, getter methods allow you to change the internal representation of your data without impacting callers. This makes programs more maintainable as you can change your design decisions without affecting callers that depend on your code. Callers can rely on the method specification instead of on internal knowledge of the data representation.