I'm having a little difficulty seeing where there is a big difference between replacing parts by policy (someone in the other thread said they put all new belts on the combine every season, John just said they replace lots of parts) vs keeping a set of belts on the shelf.   Seems like it would cost more to just replace stuff arbitrarily (and keep the old one) then to keep a new part on the shelf, at least to me. 

There is some difference between John going to a dealer 2 miles away and me going to the same dealer 30 miles away....when they're not open or don't have it in stock, or when his machine is working in my part of the world, that is negated. 

Having like machines is definately a big advantage in the parts department.  Our combines use mostly the same parts, and the last one we replaced did too.   I expect to run one more generation of machines like these, so I'm not too worried about carryover at this point.   We had quite a few belts left over in stock when we quit running 7720's.  You'd be surprised how that stock has disappeared....when you have parts often you can make something work even if you don't have the 'right' part.   Our belt usage was horrible when we cut fescue, lespedeza, and group 2 weedybeans.    By comparison corn is a lot easier on them, except for chopper and clean grain belts, those still seem to go from time to time. 

The lathe is kind of a double edged tool.....it allows you to do amazing things in an equipment down situation but it also encourages you to do stupid things when you don'thave to.