[chris vickery]

I see both sides of the discussion here. Of course vehicles were engineered to be the best they could be. It is fascinating though to look at the statistics and understand the average lifespan of vehicles due to all of the variables involved.
As Frank point out, you have Jeeps for example with "0" miles on the bottom of the Atlantic and then there are those that have survived until today with many thousands on them. I am sure planners of the day had this all figured out to include all the facets from shipping losses to maintenance to wear and tear.
If one is to study the maintenance manuals for example, these do give interesting insight as to when things like major overhauls were expected.
(when vehicles were "worn out")