Rabbi Joseph B. Soloveitchik points out a significant difference between Noach (Noah) and Moshe (Moses). When told that G-d would wipe out the Jews and make a nation of his descendants, Moshe objected and G-d agreed to grant Moshe's request (Exodus chapter 32). Noah, on the other hand, followed G-d's instructions to build the ark and gather the animals but he never stood up on behalf of mankind in an effort to avert the coming disaster. (From Moriah, cited in the Mesoras HaRav Chumash.)