It's related to the concept of Mottainai (もったいない, 勿体無い) in Japanese culture. Where any waste is considered bad, specially related to food.
replies(5):
At the end, of course, you have to throw it away - it might not be safe for staff to eat by the point it's visibly decomposing from 3 feet away. I find that just knowing the food in the case is destined for the garbage to rankle, especially when I'm simultaneously looking at menu prices and wondering why the meal costs so much; it's interesting to learn that the Japanese make those meal displays out of plastic/wax for the same reason.
Sounds like a gimmick that is way too limiting to be a general practice.