As I expected, AA is simply converting incremental 777 orders into 773ERs, which makes a whole lot of sense.
The 773ER is more capable, lower cost, and won't be made obsolete by any of the new technology aircraft - 787/350.
Two is not exactly the huge bonanza some were hoping for but the 773ER does give AA some choices for route planning they didn't have before.
Note that the aircraft won't join the fleet until the end of 2012 so the likelihood of new northern hemisphere routes with them is not likely until the summer of 2013.
These aircraft could provide helpful lift on MIA-GRU but could also be used to allow AA to start MIA-JNB; not sure if the 773ER could fly JNB-MIA nonstop but I am betting it could. Given that SAA is not a oneworld partner, if AA wants to get into S. Africa, they need to do it w/ their own aircraft.
DL is using just 1/3 of the available frequencies available to S. Africa - but I wouldn't be surprised if DL adds more S. Africa service. MIA would be a strong gateway for S. Africa.