If stores like Best Buy and GNC didn't have such good return policies, then I guarantee you they'd lose a good chunk of customers. Not enough to go out of business, but enough to notice a dent. There are tons of people out there who would rather save themselves the .99 cents or more then risk spending their money on something that doesn't work.
Apple is probably concerned about abuse of the return policy, but again if it works as the user was told it would, then why the hell would you return it?
On a side note, I know it's only 99 pennies in most cases we are talking about but if I ever went into a store with a sign "Buyers Beware: All Sales are FINAL!" I'd walk out just as quick as I came in.