Well you certainly opened up a can of worms here...Now my two cents worth. I have grown up around semis and drove them OTR and OO I have seen the class 8 trucks go from the old 2 stroke to the 4 stroke and yes there was an improvement when they did so and the improvement with the advent of computerized engine controls was also good however you now have so called deisel doctors with handheld programmers that will "tune" your deisel for a fee and have no liability implied or given. Same goes for the medium to light duty deisel trucks that are being discussed here now, why do you think the majority of these upgrade and performance items have a disclaimer attached to them, and do not get me started about these kids that like to " roll coal " I will be here till next month.
OK tyrade aside when properly maintained and used any vehicle will definatly last longer than one that is used and abused and the advantage that one has over the other also its weakness in the other so ultimatly the decision comes down to personal choice so decide what and how you will be using the vehicle, what investment are you comfortable with, what do you want.
Good Luck