Some sales aren't worth saving. One guy on this forum said he exchanged his iPad 4 26 times. 26? There's no way all 26 were "bad". That means Apple spent $13,000 to save one $500 sale. If I were Apple, I would cut off these walking obsessive compulsive disorders after the second.
Hmm... look at it from a business POV. Say you're Apple, and a customer keeps exchanging said item because it's not perfect as per him/her. After about 26 exchanges he/she is finally satisfied.
A) If you let the customer do 26 exchanges : He is happy, will spread the word by boasting how he/she was able to do x number of exchanges w/o any hassle.
You've just created brand loyalty [ in most cases ] and getting free marketing thru word of mouth, resulting on increased sales and profitability.
B) If you denied the customer after say... 6 exchanges : He is now livid. An unhappy customer will go out of his way to voice his bad experience [ forums and other Social Media are a great example here ] and may just hurt your bottom-line [ in the long run because if you're limiting one customer to a set number of exchanges, you're probably doing it with others too.. so it's never really just ONE customer ]
End result of option (B), you're loosing customers [ thus sales, leading to dropping profits.. resulting in your stock taking a hit and very unhappy stake/stockholders..] and generating a bad CS image in the industry.
Even if, hypothetically, it cost Apple $13K to satisfy one [ seemingly trivial ] it generates substantial goodwill in the long run.
However, in reality, it's not even in the vicinity of $13K to Apple. The cost of returns is very comfortably cushioned in the MSRP. The retail industry typically has a product return rate of around 20-25 %.
Finally, would you ever know if Apple took the returned iDevice, and re-sold it as brand new with a new serial number and cosmetics ?