I don't think AA miles are available through Ameritrade. Perhaps Grasshopper was thinking of TD Waterhouse (which has mileage offers for AA--not sure of the current amount).

He/she also has the mileage amount wrong for the money market account. It's 1 mile for every $10 annually. But credited monthly. Which turns into 1 mile for every $120 monthly. In fact, they cover the $50k example explicitly in the prospectus and say it earns 417 miles per month (page 28):
http://www.aafunds.com/pdfs/mileagepros.pdf