It's not just about the lost revenue by losing a few seats. You also have to add in the cost of ADDING the new seats, especially when many of their jets had just been refurbished. Furthermore, it is a justification for the airlines to continue their monopolistically high fares. I'd rather see the money spent on improviing some of the other aspects of air travel, like better in-flight entertainment, or improved meal service on longer flights.
Besides, Economy PLUS is not of much good when traveling on vacation anyway.