Logic of non-refundable upgrades with cash?
 

I guess folks might hedge with a miles upgrade after purchase, so I understand why Delta might make these non-refundable, but why apply it to those made with cash? What would be against Delta's business interest to not just let it be applied to an e-credit? Opinions?

They can potentially (but not always) be cheaper than paying fare diff -- so the argument could be they are giving you a better deal in exchange for non-refundability. At any rate, people have reported some success in getting these refunded when pleading for mercy when they need to change flights.

HUCA works for refunds on these upgrades.