I think it is pretty universal that if you request a refund of the fare drop difference, they will deduct the change fee. Also pretty common, until CO just changed, was the ability to opt for a travel credit for the full difference and have the change fee waived.

The agent I spoke with at CO was well aware that this change caused a reluctance to purchase. Stores have "benefit of sale" policies for specified periods as well as return periods. It's in the interest of the merchant/airline to get you to buy now, even if some people ask for a return of the drop in price later.