That's true. But I am somewhat skeptical about the fact that a smart person necessarily is the one with good networking skills or the one capable of forging sound relationships. There are times when a truly smart person, either due to his own eccentricity or the environment, doesn't get to have a chance of having a good co-founder unless he relocates himself which is hardly possible in many cases.
I wonder how many YC companies have failed due to a co-founder break-up.
Outside of YC, I hear a co-founder break up is one of the top reasons a company fails.