This argument borders on the ridiculous. Consider the fact that about 90% of Jesus' teachings were made to the Jews, including the following:
St. John 3:

1. There was a man of the Pharisees, named Nicodemus, a ruler of the Jews:
2. The same came to Jesus by night, and said unto him, Rabbi, we know that thou art a teacher come from God: For no man can do these miracles that thou doest, except God be with him.
3. Jesus answered and said unto him, Verily, Verily, I say unto thee, except a man be born again, he cannot see the kingdom of God.

    Then, according to the misconception highlighted above, we, as non-Jews, do not have to be born again to be Christians, because Jesus was talking to Nicodemus only. It would seem, then, that God wasted a lot of paper by retaining all those teachings that were made to the Jews. According to that, we should have had a much thinner Bible.