I started a thread about this exact same thing a couple of weeks ago. I, like you, don't get it! I took my new puppy to the vet when we got her...the vet asked what we were feeding her...I said Chicken Soup...and she said that she
strongly recommends that I feed her Science Diet, and she gave me a HUGE bag of it for free! That was about 4 weeks ago, and I still haven't opened that bag.
If you wanna check out that thread, here is the link:
http://www.yorkietalk.com/forums/showthread.php?t=44788