This thing has been talked about to death.
Firstly, ITS A MYTH that it was 80%.
Secondly, YEARS ago, there used to be a problem with a good number of people not moving on. HOWEVER, that problem was solved and recently its been smooth sailing for NYU students in terms of attrition.
BASICALLY, dont worry. I spoke to students there and they said that whole thing is not true and that the school gives you a lot of help to pass classes.