Vitamins and enzymes do begin to break down shortly after a fruit or vegetable is picked, that is true. That's why it's better to eat fresh, locally grown produce as much as possible. However, it does take time to breakdown and there's always a benefit to eating fresh produce.
Another thing to keep in mind is that produce doesn't have the mineral content it used to have, either, thanks to mineral depletion. That leaves us all to find different means to get what our bodies need to thrive in this polluted world.