I'm with DuckFlyer on this one! In regards to baliktad comments, when it comes to a passenger changing a reservation there is a cost to the airline. And thus they have to re-coup these costs somehow. However, I generally do not agree to the level which they have set their change fees. I think $75 to change a reservation when the original fare amount (excluding tax) is in the region of $89 is gauging the customer.
In regards to overselling, I cannot say that it's an unethical practice since they clearly state that this may happen in their conditions of contract. In fact we all benefit from it with lower fares.