Paul,
If you've ever read the history of the ground wire and how we progressed from ungrounded to grounded, the same rule applies: It would only be important in the event of a problem, therefore, proper trade practices installed by competent tradesmen mean those breakers are unnecessary.
We don't count mice, heat, age, deteriation, etc.. You see, we didn't tell you, but in THIS country we have none of those problems.