That's a silly argument. "Don't document, because it will never be up to date."
Yes, the developer documentation should be updated with best practices. Remember: the code itself is intended to be self-documenting (through the magic of ad-proc). Meta-information like best practices needs to be done out of band.
Documentation is a cultural issue. Once developers get into the mindset of "Fix the documentation when you fix the code," the documentation task is no longer onerous.
