Age is an undependable factor in determining validity. While we don't expect authoritive texts to be true all the time, we call them authoritve because we understand that they have a higher standard involved in their creation that most other publications. Small experiments that may or may not have been peer reviewed or had proper rigor applied to will not be included in the encyclopedia, which itself realizes that it needs updates on a regular basis. The higher standard that applies is comforting to know especially when dealing with what may be affecting somebody. Understanding that what is written in that specific text has a time-tested history of being accurate, and even mentions when links are only causal and should be attributed to greater issues is of incredibly high value. There is no point in treating it with a high degree of skepticism simply because it has earned a reputation of being an authoritive text - that's paranoia for no real reason. Understanding that the text can be flawed, because we are constantly advancing our comprehension in these fields, is one thing, but dismissing something entirely because of a conspiracy theorists attitudes about institutionalized knowledge is pretty foolish, especially for something as widespread and with as much proven value that the DSM IV TR has demonstrated.
Also, if you're going to cite authoritive texts that have been proven false, list the examples. otherwise, setting up strawmen is a pretty shitty way of proving your point. It's of my opinion that intellectuals should consider and weigh all ideas, not simply challenge them entirely out of habit.