However, it isn't ALWAYS 98% of what our body needs to be replaced in a situation a sports drink (vs. energy drink) would be appropriate.
I do agree that water is a GREAT drink, in fact (discounting good scotch and beer) I could live the rest of my life drinking nothing more then coffee and water as my day to day drinks. And if you are able to eat appropriately and actually are eating appropriately, water is typically all you need for proper rehydration during periods of intense work. However, this isn't always possible.
I break down sports drinks into 4 categories:
The first category is
JUNK!. This category includes all the energy drinks that really just soda with more calories and caffeine, soda and the so called sports drinks that have minimal electrolytes and are basically soda minus the carbonation. Now, these drinks can still serve a purpose... I can testify to the miracle like properties of defizzed Coke during the run leg of an Ironman distance triathlon and while I can't say Red Bull gave me wings, it did help me find my running legs at more then one Ironman.
The Second category are all the low calorie drinks with appropriate electrolytes. These drinks, like NUUN, CamelBak's hydration, PowerBar Electrolytes, and SportsTabs, will provide the user all the hydration and electrolytes they need, but if they want calories they need to look elsewhere. I like to use these drinks for short (under 60-90min, depending on the intensity) work sessions or during LONG LONG work sessions where I want my calories in solid form.
The third category are the all in one drinks that have good calories and electrolytes, but are still mostly hydration drinks. Gatorade endurance (before it was discontinued) was barely in this category but drinks like PowerBar Endurance, Clif Shot Drink, eFuel, and Hammer Nutrition H.E.E.D. (my favorite) will supply the booth the electrolytes and some calories along with hydration for shorter work periods or as a supplement to more complete nutrition in longer work periods.
The forth category are drinks that have the primary purpose of fueling (providing nutrition). The protein and higher calorie counts make these drinks basic especially useful in long work periods where the intensity level is high or liquid nutrition is more convenient then solid nutrition Drinks like Hammer Nutrition's Sustained Energy or Perpetuem and Accelerade.
Now that is probably WAY more complicated then most people need or want to think about for hydration... and in the end (and my opinion),
NUUN is probably the perfect hydration/sports drink for most peoples needs.