This is limited to 1 specific credit card which is otherwise highly undesirabe -- the Amex Skymiles card. It doesn't apply to any other card, and technically is not an announced card benefit but only for 2014. So 99% of DL Skymiles members will have to qualify using dollar spend on DL flights.

When will QFF add a similar dollar spend requirement? Fwiw, DL is affiliated with Virgin, so it hits a bit closer to home than otherwise.