OK, I don't know if i am getting this mileage plan or if this is a thing of beauty. But I noticed today if i booked a flight from ORD to ANC in Febuary it would cost about 600 bucks. I noticed that it's 20,000 miles to book award travel and you can purchase 20,000 miles for 500 dollars. How can this be possible and is this correct or am i missing something

Any help would be nice