This is not IDB. That happens when you are denied boarding on a flight that leaves due to an oversold, or some other, consideration. This is a simple mechanical issue. The usual procedure is accommodation on the next flight and overnight accommodations, if required. In this case, they gave you a shuttle bus.
I think that the $75 was fair, all things considered. If you complain, you may get some miles. You may even get the $75 re-offered. But do not use IDB when you do as this does not apply.
Cheers.
You're right, it's not IDB, but I disagree that it's neccesarily fair. If a person wanted to drive from LA to Santa Barbara they could have done just that instead of booking a flight. It certainly is at least 3 hours for that 90 miles, when traffic is low. AA had a contract to fly them and didn't do it. They should shuttle them AND refund that portion of the ticket fee. If that is more than $75 dollars they should refund more than $75 dollars.
What is it with airlines that they don't understand the basic nature of a contract? Of all the businesses in the world it seems like airlines are the only ones that don't think they need to abide by basic contract laws.