Originally Posted by
LlamaJesus
They're constantly 10-15% (I think there's a specific, consistent percentage but I forget) cheaper than AA directly due to some not-very-well publicized agreement between Amex and AA, which I believe was linked earlier ITT. I'm assuming this is the reason you're seeing a fare difference anyway.
I am seeing ~5% for flights at the end of the year (past the stated 5/31 end date).