Amex gets around 2% from large merchants; not 3-7%.

Not all of the merchant fees are profit; they do have expenses such as buying points, establishing and maintaining an electronic network, customer service, employees, etc.

Delta miles are darn near worthless at this point (well to be more exact I value them at about half the value of just about any other US carrier's miles) and the only thing I have found halfway decent value with them is using them to "pay with miles" on your credit card, making them worth 1 cent each. So if you plan to do that and to redeem all of the miles you earn before you cancel the card, then the miles are worth slightly more than the credit. But either way you are getting something for nothing and yes, it is a very good retention bonus. In fact they offered me almost nothing, a $25 credit I think (but I spent nowehere near what you did on that card). Now without the card and ability to use the miles for .01 each, I am getting out of the Delta miles business altogether. Not worth the trouble.

I've attempted to cancel two cards so far this year. Both times I got an annual fee waiver...once I got a little teaser bonus on top. (Spend $x in 3 months, get y.)

So if you use DL and genuinely have an interest in the card, I'd probably accept the fee waiver. If not...you already have SPG Amex, which is a superior card anyway.

Ditto. Called to cancel UA MP card and no waiver or miles offer Only offered to downgrade me to a fee free card

that's a pretty good deal....

Called again today and they said they had nothing to offer. The CSR said that the system had "no current offers" and her manager said they had no idea why the system offers some people offers to stick around while others are offered nothing. I've spent more than the $70k as mentioned by the first member in my first year. Any ideas?

I would take an educated guess that Amex knows exactly how much money they make off of you each year, and that their retention offers are based on that. Just because you spend $70k/year doesn't necessarily make you a very profitable customer. You may have large percentage of charges at merchant types that are at the lower end of the discount rate they charge you, leaving little in the way of profit. Perhaps you always pay your bill in full each month, and always on the Payment Due date, thus maximizing float costs while never generating any interest revenue. Perhaps their assessment of the chances of you defaulting eat up any remaining profit. Considering the amount of data they have, I bet they're very good at deciding what offers to make.