If everything is as you say it is, it's indeed an interesting situation. One possibility that it brings up is Amex has certain accounts that are either unprofitable on the face of them, or perhaps marginally so once bad debt risk is factored in. I've wondered about this myself from time to time.

Generally speaking, it's not at all unreasonable for some consumer-oriented programs to be unprofitable to the vendor for a certain subset of customers. As long as that population is small, and it's not prone to abuse, it can be perfectly fine as long as the overall program is profitable.

Here's an example of what might be a "worst-case" scenario for Amex for a customer that has a perfect payment history and an excellent credit record: a Starwood Amex cardholder that charges a large amount near the beginning of every billing cycle and pays in full on the due date. For that situation, Amex has to float the charges for about 7 weeks without collecting any interest. Also, unlike an MR-earning card, the Starwood card earns SPG points immediately upon the close of the statement. So, unlike MR, an SPG Amex 1) pays cash to an outside vendor immediately upon close of the statement (even before payment is made), 2) there's no breakage, 3) there's no chance that the cardmember will redeem for merchandise that costs less than the settlement costs to SPG, and 4) there's no float.

I could easily see that some SPG Amex accounts are not profitable to Amex, depending on some of the numbers that we don't know. And even if they are all at least marginally profitable, I can see how some with razor-thin margins may not actually be profitable once bad debt risk is taken into account. This being the case, it does not surprise me that Amex might want to bribe certain customers to close their account. I'd like very much a fly on the wall when these issues are discussed and decided upon internally.