Now it makes complete sense. For reference, here is the link to the avoided DCC attempt at the Taj Exotica Maldives. If they had charged you in HKD you would have lost nearly 6000 miles. While in the US rewards earnings don't really matter and the only loss is the DCC markup, I think the above point from percysmith needs to be emphasized and can help us win the messaging battle against DCC.

While some people don't care that they're getting ripped off on the DCC for the "convenience" of knowing the charge in the home currency, I think most people would go completely ballistic if you told them there's the possibility that if you accept DCC that you won't get any rewards for the transaction. (That's presumably why the person is using the card in the first place.)