I think that there are a couple things in your math that don’t add up completely.

The first is that very few people are paying 1.5 cents per mile. Certainly the vendors buying the miles in bulk, namely AmEx from Delta, are paying WAY less than that. The consumer may pay more, but they are a much smaller volume of miles, so the spread isn’t as high.

The other bit is the double miles availability. Delta is now apparently increasing the cost of those 20% (25K -> 30K each way). For the premium tickets they’re going from 200K just a few years ago to 300K this year on Continental (or at least they were supposed to). That is still way less than a full J fare in the summer from NYC to Paris ($3000 at the 1 cpm number), but it is a huge increase in the cost for redemption. And the switch to this flat rate penny/point plan makes those rewards incredibly expensive from a redemption perspective.

And just because it took Delta 2 years to copy United doesn’t mean that the next one will be so slow. It only took US Air a couple weeks to copy the charge for the second checked bag. And there’s no telling how long the next one will take.

The carriers can’t afford to kill the cash cow that is their FF programs, but they also can’t actually afford to keep selling so many seats below cost or a lot of the other things they continue to do, and no one can tell how they’re going to try to make it up.

I hope you’re right that they don’t kill the redemption options, as I take advantage of it too, but I’m not sure this going to last forever.