There was a story that checking ID's on plane tickets was at the top of the airlines lobbying wishlist after 9/11 so they could curtail the practice of people selling unused tickets to another (same gender) person.
I've never completely understood why this was the case. If I'd be theoretically capable of finding a friend (or even complete stranger) to sell my plane ticket to if I found I couldn't travel, then it should be equally easy for the airline to do so. And yet, refundable fares are often significantly more expensive than non-refundable fares.
I can certainly understand and support some kind of monetary penalty for breaking out of a reservation, but it seems like airlines err too far on the side of making you think twice before canceling or changing your plans after the initial 24h window is up, and penalizing you heavily if you end up doing so.