Well, it's not like the world revolves around what some particular individual does. Other people might be more clumsy. Or might live in places with frequent rains (from London to the tropics and India), do all kinds of stuff outdoors, etc.

Many people approve of a waterproof phone. And in any case, it's a nice feature to have even when you don't need it. It gives piece of mind for using it to call in the rain for one -- and if you have ever been outside in London or tons of other places you'd have seen the utility.