I'll admit that AA has called my bluff on this a handful of times.

I fly DCA-SDF-DCA rt at least weekly, and the one-ways have consistently been $132/136. But every now and then there's a flight on a given day that's at $233, $283, etc., even though it isn't sold any more than the other flights, but it ends up selling out. Happened last Sunday -- I of course bought the cheaper earlier flight and did a same-day standby onto the $283 flight, but I only just barely cleared, and (for the first time in 66 of these segments) I didn't make the upgrade.