BOS-LAX is a competitive market with JetBlue, United, Alaska and AA all flying nonstops (unusual for Boston where on most routes there are at most two carriers on any given route). JetBlue prices Mint starting at $399 (most flights offer some seats at $599) so I'm guessing that the competition is forcing the AA F fares down, and that this example is route-specific, probably not indicative of a broader change.