That's not really accurate. Yes, the total amount of food may not change, but the type of food changes quite a bit. People will eat less desirable, but cheaper food.
The article mentions that it would be better if some of the farmers started growing vegetables rather than grain, but the subsidies don't pay for vegetables.
Same for wheat - low gluten types are cheaper. (Which is basically why they invented the http://en.wikipedia.org/wiki/Chorleywood_bread_process )