What is meant by true/enforced privacy is that the only way to access something is to modify the original source. This is not the default anywhere else, as you know, but is encouraged by some (Crockford for example) in Javascript.
Enforced/True privacy is very bad, and the badness is multiplied by the fact that in Javascript it cannot be fine-tuned so when you are making it private for random application code, you are also making it private for other internal classes.
Those warnings are not part of the language, and can be done with underscore prefixed Javascript too in your build step, a fine example of programming into one's language.
