An 8000hr design life means that 10% of the units will need something major (engine/trans) in the first 8000hrs.  The reality is Deere knows the vast majority of machines will never reach 8000hrs so why design for longer?  Given 400hr/year for 20 years is 8000hrs why design extra life into a machine that will reasonably be replaced in that time frame in favor of better technological developments.  Some companies use design life that is much greater yet they sell far fewer machines than Deere does; pretty easy to see which company is making more money.

The realilty is agriculture equipment has much lower life expectancies than other industries and it part of what makes ag equipment reasonably priced.  Take a gearbox as an example where ag pushes 200hp thru a gearbox that the industry rates at 75hp; if it lasts 1000hrs in the ag application it is suitable for most ag machines however, some industries will expect 40-60,000 hours out of that same gearbox at the 75hp rating.  There are charts showing repair cost as percent of initial purchase price for various pieces of equipment.  The only thing considered over 3000 hrs are tractors.

And to answer your question:
What industry other than agriculture would find an 8000 hr life acceptable?
Automotive, where 8000hr would be 280,000 miles which is about where most vans, sedans, suvs puke out.  Yes some pickups go longer, but even the vast majority of pickups are considered worn out by 300,000 miles which greatly dimishes their value.

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