Say what? This is like saying that once you know what all the commands in Illustrator do, you're well on your way to being a professional illustrator. The reason that K&R is so small is that so much of C programming happens outside/above the language.
I like K&R a lot, and I won't argue that it's the best soup-to-nuts C book (though I recommend C Interfaces and Implementations more heartily). But if everything you need to know about C is in K&R, how do you implement a balanced tree?
(I caught myself typing "how do you implement a hash table", and remembered that K&R actually has a hash table in it. Damn you, K&R!)