International airfares are directional whereas domestic airfares are reciprocal. The published fare for a round trip journey NYC-LAX-NYC is the same for a round trip journey LAX-NYC-LAX. In the case of international fares, airlines are required to file published fares from each country of origin with the respective government of that carrier's destination. Thus, AA's published fares from Argentina to the US are different than AA's published fares from the US to Argentina, whether they are one way fares or round trip fares (and the same goes for AR, UA, DL).
As an example, a round trip economy class (restricted or unrestricted) fare EZE-JFK-EZE, outbound 24/02/2014, inbound 10/3/2014, with the US as country of residence, is $1632.00. The same journey with the same type of fare JFK-EZE-JFK, with the same dates and country of residence, is $1415.00.
Using the same dates, same type of economy class fare and same country of residence for a DFW-LHR-DFW and a LHR-DFW-LHR journey, the fares are $1039.00 and $989.00, respectively.
Using the same dates, same type of economy class fare and same country of residence for a JFK-LAX-JFK and a LAX-JFK-LAX journey, the fare is the same whether the origin is JFK or LAX, $952.00.
I was an international air tariff analyst for 35 years before retirement. I did this work for 14 years with several different airlines, then for 20 years with American Express. In all of those years, never once did I encounter a published international airfare (regardless of class of service or fare type) between two international city pairs to be the same in each direction. International airfare pricing is comprised of a wholly different set of rules and regulations in contrast to a country's domestic airfare pricing rules and regulations.