Well, I think I have found the reasoning behind the denial of the miles. I read down further in the terms and conditions and found the section of "Earning Exclusions." Under #4 it states, "Voluntary flight changes in lieu of non-stop and/or direct flights for the accumulation of additional mileage is not permitted." I am assuming this is why my flight to ATL from DFW was not counted in the mileage accrual. Oh well, I guess we live and learn.