I suppose we can't overlook the convenience factor. On the other hand, unless you absolutely need it to come out of the original carton and/or don't have access to water, there's no way it can be a good value simply from the standpoint that it will always be cheaper to make it yourself. Maybe they just don't like having to stir something together in a cup? I wonder how they drink their Ovaltine.
That said, you bring up a good point about the health angle. They do point this out all over the carton, and you've pretty much summed up their reasoning. I think the whole thing is brilliant and at the same time it just makes me shake my head. Of course it will be healthier than regular orange juice from a pure calorie content standpoint. When you water something down, it'll have less of everything than whatever it was you started with.
Like I said, brilliant. They take the same product, water it down so it costs them theoretically 42% of what it would cost to make the same volume of normal orange juice (minus the advertising and package design budget--which eventually get paid off, the nominal cost for the water, the cost of the sweetener, etc.), sell it for presumably more than 42% of the cost of normal OJ, promote it in a trendy, health conscious way, and rake in the bucks.
And consumers, merely reading the carton, think "Healthy! Good! Bleat!" and buy it. The box says its good, and of course, the almighty box is always right.