i worked in Major Sales (electronics, etc) at Csotco. Oldest TV i ever approved for return was an almsot 6 year old Sony 42" Plasma. They paid $8k for it but since they didn't have a receipt we gave them the most recent price int he system which was $5. They bought a 50" Pioneer and put like $2k in their pocket.
There are ways we can deny certain returns other than computers. I know every way to return something to costco and even the rule with computers/laptops can SOMETIMES be broken under certain situations but it goes against the costco written policy.
costco makes a lot of its money (i have heard fumors of 55% up to 95% lol) from membership dues. But also think about it this way, say you buy a TV for $2k and you keep it for a eyar and return it for another model. You are seeing it as costco just lost a ton of money when in fact they invested your $2k throughout that time, whether it be in stocks, mutual funds, whatever, or towards purchasing other costco products such as food that makes a profit. By the time they lose money on your return they have most likely turned a profit on your original purchase and see very little to no loss at all.