A_D is sometimes extremely terse.
"Oberoni Fallacy (noun): The fallacy that the existence of a rule stating that, ‘the rules can be changed,’ can be used to excuse design flaws in the actual rules. Etymology, D&D message boards, a fallacy first formalized by member Oberoni."
So, saying "A good DM obviously wouldn't go by the rules as they are written" is not really an excuse for the rules being poorly written.