if it was done on purpose, to take advantage of their stupidity . . . . .
the image of the receipt the OP posted for the original purchase outlined what the return values were. if they returned it without a receipt on purpose, to take advantage of a hole in their system . . . . .
if the cashier got in trouble for it, or someone else did, that isn't right, because it is a hole in the company's policies. but that would not stop it from happening.
on the one hand, i think that a big company like HD should know better. but, as bill nye said, consider the following:
you bought a battery there for 89$. you got it home, and found you could get them online for 50$. of course you want to take the more expensive one back. but you can't find the receipt.
you want HD to be nice, and take it back, even without proof, right? but this is a huge hole for them. they dont put tags on most things anymore, since it is wayyyy too expensive. but what happens when you bought it from the Big Box Hardware store, and lost the receipt, but they won't take it back without one? is it moral to go to HD, and get them to take it back?
but i bet they know about that. and they think that the small amount of money involved, for things that they can resell anyway, is a small price to pay for the positive customer relations it generates.
in my book (out soon on Kindle!

, the error was when the OP decided to share it with the whole world. if he hadn't, HD would have continued along, happy with their policy. at this point, now that this has been widely disseminated, (and i bet they hear about the things that a widely read board like this traffics in) i bet they are going to consider changes to the policy.
hopefully, they will do something innocuous, like having the CS people look up the original transaction in the system. HD will keep them for some limited period, like 90 days, and if the CS person can find it they will refund what you are owed, based on that receipt. if they can't and it is small enough amount money, or they see how much you are buying, and decide that it isn't worth ******* you off, they might, otherwise they won't.
of course, there is another issue. are the CS people going to be able to see what you bought in other, nearby stores (in case you bought it two towns over, cause they had it in stock, and the close one didnt)?
these things get complicated quickly.
it was bound to happen at some point.