Should have gotten a chase taxi following you.

Ive only had to use the "flat tire rule" one time, LAX-LHR b/c of a massive pile up on the 405 - but I called from the car stating that I believed I would miss the flight, and the EXP desk protected me on a later flight.

Interesting point. My guess is if you call from the accident scene explaining what is going on and that you dont know if you will make the flight, they would be apt to work with you. Keep in mind you can be protected on another flight even while the original flight is still in your PNR. I've had this multiple times when flights get delayed for a mechanical, and limited options to rebook. They'll throw the other flights in as a reprotection and they disappear (apparently) if you make the original one.

AA has a large presence at ORD. I would have tried other agents.
While they are not required to offer you standby, it does happen.

Yes.
What considerably helps in these situations is calling AA (EXP desk) to protect you as soon as you are aware that you might not make the flight and inform them of the fact.
I got stuck in DFW traffic once (huge accident) while driving to the airport to get on DFW-FRA and they rebooked me on next days' flight without any issues or charging any fees, leaving even the upgrade intact once I got to the check-in counter at T-17, way too late for anything.
Another time I missed the train from Basel to Frankfurt and had to drive up there which takes more time than the high-speed ICE train even with unrestricted autobahn speeds. Called them right away and they kept the counter open waiting for me to check my bag until I got there, well after the deadline (52 minutes until departure).
And yet another time I checked my bags curbside at LAX for a flight to LHR, then when I wanted to drive away and return the rental car the POS thing wouldn't start anymore. Waiting for assistance took too long, so AA rebooked me on a later BA flight with no problems and no fees (agents had quite a field day joking about how I'd fend off all the overeager traffic cops handing out tickets like candy for cars remaining there longer than thirty seconds).

This is one of these things where having status *really* helps.

Wow, it sounds like there is definitely the possibility of AA helping out EXPs in these uncontrollable situations. Really bummed that we had to shell out the $400. I am going to take the advice and write to customer relations. Especially since I now have nothing better to do today as I was intending to be laid out on the beach by now :(

AA did a huge favor for OP by not cancelling the entire itinerary and requiring him to buy a new RT ticket at walk-up prices. There has never been a Flat Tire "Rule", even less so on intl. It has been an unwritten policy.

The change fee (2 x $200) is the least expensive option and OP ought to thank AA for having cut him slack.

This was also the result of an accident and the change fees themselves will likely be covered under OP's travel insurance (as would the reissue tickets if that had ocurred).

Your story angers me. That $400 would be better spent with Red Rum Cabo trolling the ocean for DINNER.

In reality - you should seek compensation from the taxi company. Or the insurance of the guy who hit the taxi you were in - they're the culpable ones here...

I completely agree here. I've had great luck when calling ahead. Especially since you have same-day standby with EXP.

Could you have shipped the luggage home and bought new stuff in Mexico for less than $400? :)

I had asked about us going standby and we were told it wan't possible since the flight wasn't within the US or Virgin Islands. I didn't know enough about this to question this statement. Also, the agent mentioned all the flights were sold out so we were likely to get stranded in DFW even if we were lucky enough to get on a flight out of ORD.

I actually asked about shipping options in my desperation (to Mexico as I didn't think about shipping home and replacing). There were no options for shipping.

As others have suggested, I would send a polite note to Customer Relations:

"We certainly appreciate the EXP desk assistance earlier today and while I understand the reason for the change fee charges, we would like to request those to be refunded/waived due to the circumstances we encountered en route to ORD. Thank you in advance for the consideration!"

Yup. you almost took the exact words out of my mouth. I sent a very similarly worded email to them a short while ago.

It will be a pretty likely response of "Well we normally dont do this, but since you are such a loyal customer we'll make this ONE TIME exception..." I cant tell you how many ONE TIME exceptions I've gotten from AA. I guess its there way of at some point saying NO without me going onto FT to complain :)

I sincerely hope you are right. I'm hoping that I get a sympathetic ear from whomever reads my note.