i think for most domestic flights, fares are priced one way and RT's are simply twice the one way price. It's just a function of AA opening the lower buckets (Q,N,O) up for one way purchase. Intl I think the lowest one way bucket is H. There isn't really a premium for one way as much as AA not selling you a OW in the lower buckets.
Of course, if all you buy are full fare tickets, then buy OW to your heart's content, no change fees, fully refundable, no restrictions...