Carbs are pretty important post-workout, for things like glycogen replenishment, insulin release, and providing more of a stimulus for protein synthesis (when consumed with protein). For more detailed info, on this, and much more, check out the articles in the Article Library by Dr. John Berardi and David Barr.
Surge has the perfect ratio of carbs to protein. It also has the fast digesting carbs and protein, which is what you want at this time (as opposed to the casein in the canned drink).
Also, sure, 50 grams is nearly half your daily intake, but the hours post workout are when you best tolerate/should be consuming them. So, in reality, it's okay to have a 50 gram serving around your workout, and continue your normal eating after that (preferably protein + carb meals, with the rest of your daily allotment of carbs evenly spread out).
That's a pretty simplified version of what and why, so if there's anything I've left out, please ask!