This is a very interesting article. And while it is true that cats in nature eat a high protein diet, don't forget they're ingesting the contents of the stomach of the bird or mouse - which has grass and grain in it. Also, cats do drink water. Finnicky cats often only like moving water - thus the water fountains. But for cats that won't drink, wet food often provides the hydration they need.
We let our cats free feed on dry food, and we feed them one meal of wet food a day.