I just had the opposite experience. I
reported yesterday my frustration at Expedia offering an N fare from the UK that was $40 cheaper than the S fare on aa.com. I put the S fare on hold until today. This morning I discovered that aa.com was now pricing the itinerary using a W fare that is $70 cheaper than the S fare!
I got a message with the plausible but misleading explanation:
Price Change Notification
The price of this itinerary has changed since you selected your flight(s).
This happens because seat availability often changes based on demand for a particular flight.
The lowest available total price, including taxes and fees, is now:
The UK aa.com pages had been advertising a "Spring Super Sale from the UK" until March 20. Yesterday they were N fares (including the one on Expedia but not available on my flight on aa.com). Today the same page with the same introductory blurb is now listing cheaper prices with W fares!