The simple answer to that point is that clothes can be removed at the end of the day. That's why cases like the Blockbuster one are different from what you bring up. It's an undue, unfair burden to place restrictions on persons of one gender which apply at all times, while allowing the other sex complete freedom from such restrictions.
Nobody's talking about men wearing pantyhose or women wearing three-piece suits. Because of the somewhat unique nature of hair in this sense, as something which is not immediately replaceable, this issue stands apart from other gender-dress code questions.