Backflow preventers are a safety device, that, should they fail can compromise the health of a whole neighborhood. So, testing the mechanical devices that WILL eventually fail, is a good thing. It's in the same line as (at least in most places) getting your car inspected every year or two. Especially on a new car, is this really necessary? Probably not, but it's still required, because failures DO happen, and it can affect not only the driver, but his passengers, and anyone else on the road at the time of a potential problem.
Our insurance requires annual inspections of our fireplace flue, even if they are never used. Lots of things like this in our society...it's one of the prices of continued safety for all, like it or not. Bitch all you want...probably won't change the result - inspections can save people from themselves.