To me, the 'protection' concept makes some sense in theory at least. Look at the extreme case of Barry Bonds in the 2002-2004 seasons. In 420 games he was walked 578 times, including 249 times intentionally. It seems reasonable to assume that he would not have been walked this many times if he had a hitter as good as him batting behind him. Of course there weren't any other hitters as good as him.