The whey vs food thing is over thinking. While Stevesmi is technically correct a LOT of food is in a far less than natural form. For example a burger is GROUND as opposed to being a piece of meat in its previous form. Yet, to use Stevesmi's example, you'd still get something nutritionally speaking from that frozen OJ. If we didn't we'd all be a long time dead.
That said is it ideal or optimal? No. Drinking a whey (ideally an isolate) is a convenient way to get protein in. But, in a perfect world, you'd eat a small high protein meal.