It's just another proof that AA does react to the things we FT'ers do. Not only do they leave in the Sat. night stay, AA also inserted the no-return-on-Sunday rule.
And check out these annoying little details....
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Fares do not include September 11th Security Fee of $2.50 for each enplanement that originates at a U.S. airport, up to a maximum of $5 per one way or $10 per round trip. </font>
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Government taxes and fees of up to $108 USD, varying by destination, are not included, and may vary slightly depending on currency exchange rates at the time of purchase. </font>
Still, $670 from Boston isn't too bad of a run, and spending a day in Tokyo could be interesting.