Sorry, if this is a naive question, but I could not find the justification in any of the major text books like Bondy-Murty, Diestel or West. Perfect graphs have many beautiful properties, but what is the single reason they are called perfect? Or is it just a aesthetic preference by Berge?
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perfect graphs were first motivated by information transmission theory originating with Shannon ie Shannon Capacity of graphs. they are called "perfect" by Berge because they can be used to model a noiseless or "perfect" information channel wrt transposition errors in transmission called "confounding". from intro in  which also has a very detailed history in the 1st chapter cowritten by Berge.
 C. Berge, The history of the perfect graphs, Southeast Asian Bull. Math.
20, No.1 (1996) 5-10.