The issue with that, is there is no idea how old the watch actually is when it arrives. As with everything, people tend to think of something having a 'birthdate' of when they acquire it, when the truth is a product could have been sitting on a shelf for quite some time first. With watches in particular, this is the issue. When cars are sold on, there is paperwork, a checkable mileage etc, which tells precisely how old the car is, and how much it has been driven, making it easier to predict and schedule servicing for it. Someone could buy a watch 'brand new' from any dealer today and receive it say saturday, but that doesn't mean the watch came off the factory floor yesterday, it could've been a week, a month, a year ago, and that is why waiting the 'initial' 5 years, might mean the watch failing before that 5 year prediction
[Edit to add]
Personally, I am not in the habit of paying the cost of another watch, having a watch I have just received serviced, but, I can appreciate the wisdom behind doing so