The fries don't degrade because they were dessicated during deep frying, that is, all the moisture was driven out. The large fries retained a lot of moisture during cooking so rotted rather quickly. They will last practically forever unless they get wet, the same as any other dried fruit or vegetable. But you really really wanted to believe it didn't you?

All that oil, is very good for you, eh? Watch Super Size Me and then go to McDonalds and eat, if you're so ignorant!