My guess is that fare change costs are merely one of the several dependent variables AA rules / RM folks take into account when establishing fares. They might imagine we will read the detailed fare rules and decide how much risk we are willing to take and how much we are willing to pay to avoid that risk - even though I suspect most people merely see the lowest price and pull the trigger, particularly if they fly infrequently and primarily for leisure.

Others check the detailed fare rules using ITA or ExpertFlyer, or even AA (though one certainly isn't presented with all the fare options on aa.com,) and then book, perhaps using the telephone CSAs or putting on hold and calling Web Services and requesting the fare class they see is available with the features they prefer. If one doesn't want any restrictions attached to their fare, that's a considerably more expensive product - which there are obviously customers for.

How much is too much? When people won't pay it, it's too much - but flyers are a bit of a captive audience, and I'm sure only a minute percentage educate themselves via websites, etc.