Delta doesn't care whether or not GUCs clear and they consistently make every effort to reduce GUC redemption rates (insanely discounted D1 fares during low demand periods, shrinking D1 cabins, etc).[/QUOTE]
I'm not sure. I think they may care more about their GUC program having at least *some* real opportunity for upgrade, and not totally pissing off their best customers, more than they care about this one very small revenue stream of DOD upgrades at one airport. And, if for any reason KL was trying to sell these upgrades before clearing GUC's so that they could earn more revenue, I could see that upsetting DL.
Plus, I think you
ethernal was right to question the idea that DL is trying to protect their product here. ~$600 + 25K miles (so for arguments sake $850) for a one way upgrade is really not, as ethernal said, a super discounted price compared to advanced purchase fares. It's a good deal, for sure, but if you think of the r/t price of that $1K coach ticket plus $850 each way (which I know you can't actually do), you are at $2700 for a TATL J ticket. A good price, but findable with an advanced purchase.