As an aside, I really don't understand why companies often pay more than the statutory minimum for redundancies. Is the excess payment simply a form of a protection money to prevent their former employees from stoning their buildings or what?
No, it's because the current/remaining employees are at risk depending on economic circumstances. It is a payment that says "work hard, don't worry, if the company lets you go, you'll have enough to tide you over until you find something else". Companies that are unnecessarily tight with redundancy money find staff turnover rises in my experience.