That is correct. It's been that way since they switched to SkyMiles in 1995. Prior to that they counted all miles from all sources, as AA still does. They grandfathered all the "all miles" totals into the new program but counted only flown miles, including minimum flown miles credit for short flights, from then on.

So, putting the tax bill for your Powerball grand prize on a credit card won't get you a bit closer to lifetime Delta status. Of course, if you win the Powerball grand prize, you can buy your own 767 so it wouldn't matter.

(Confirming just to remove any doubt left by the "I think" in the quoted post.)