I commented on some of the policy arguments that the Woolley court relies on to support enforcement. The court's distinction between individual contracts and policy manuals distributed to the entire workforce arguably cuts against rather than in favor of enforcing the handbook. And purported benefits from avoiding unionization may flow from preventing arbitrary discharges, but the existence of those potential benefits doesn't really signal that the employer meant to extend legally enforceable just cause protection. In my view, the best argument for enforcement is that the employer has a comparative advantage in bearing the risk of misunderstanding. On balance most courts have decided to enforce manuals unless they contain a clear confirmation of at will status or a provision saying they are not intended to confer contractual rights.
Many courts also refuse to enforce if the alleged promise is too vague and indefinite.
Promissory estoppel depends on reliance. Bargained-for consideration requires that promisee at least know of the promised protection. As the note case Weiner suggests, reliance on the manual will often be required. As you read, Woolley presumes reliance. Thus the court relies less on formal doctrine than on its sense that public policy supports enforcement.