I'm confused why one would want to do this... maybe I need to be spoon fed. I'm guessing if you were going to sign up for the Delta card, get the points, then cancel the card this would be useful as you would no longer be able to use the pay with miles feature.

But why in the world would you want a $1,700 e-cert? If you had 100k skymiles you can get a roundtrip ticket to Europe in first/business. Which usually brings the worth of the skymiles over 1 cent per mile. Wouldn't the only positive of using this method would be if you were planning to cancel the card or would the e-cert be able to allow one to earn miles on flights purchased with the e-cert?