The point being that many hikers will clean out their dishes with their tongues or fingers (to save water, weight, etc.), get sick, and then tell everybody it was the water.
Good point - we take so many precautions with our water, then do crazy things like inventing 5-second rules when a piece of food drops on the ground (if it lay on the ground less than 5-seconds, you can still pick it up and still eat it) or the saying, "God made dirt and dirt won't hurt".
Actually, as far as the water goes, I don't treat water because it has dangerous pathogens in it. I treat it for the reason that Brum gave about water in Mexico. If your body isn't used to the "benign" micro-organisms in the water you're apt to get cramping. Maybe cramping is too nice a word...maybe a more appropriate analogy would be the pain of giving birth to the alien in the movie of the same name. Hey, you'd think that water coming from snow melt would be free of nasties, right? Well, it is, but if the bugs in the water aren't the same strain as the ones in your gut...ugh! If you experience this just once, you'll see that a few dollars worth of chemicals or equipment is well worth the peace of mind.