Things can get brutal in art school indeed! I think that a big part of this (and its one of the parts that would be less tolerated in say, and engineering school) is that there can at times be a significant political dimension to the criticism. That is to say that the critiques are nominally focused on such and such a technique or choice of subject matter, but are actually about aligning oneself with a faction advocating the trend du jour or that one professor who hates anything X. Having said that, this sort of stuff certainly happens in business settings as well, which supports GGPs point.