Guy, I don't think people are questioning your method. It is a good way of doing things, but not the only and not always the practical way. And I am having a hard time following you as well. You say if your back goes down, you can get another the next day. I am sure you can do that for the body. So it does not look like it is actually a big deal that you have a backup, apparently I can get a whole new camera sent to me--BTW, with all the problems you have with Phase/Mamiya bodies, I am glad I did not go that route.
But you also do a form of commercial photography that cannot be applied across the board. I have known a lot of LF landscape photographers that never carried a second body in the field. The weight and size just does not make it practical and a smaller backup system does not solve the weight problem nor address the quality issue. Commercial photographers have the luxury of packing heavy. You also have clients on the set/location looking at watches so time is really important. Not every form of photography has those constraints nor budgets.
Also in this discussion we are forgetting equipment cost. I could get two Pentax bodies and a lens or two for a Phase IQ140 back. We can argue which is better to use, but if a backup is really important, I could have my cake and eat it too. The S2 changes that equation. There are all sorts of ways to add up to a solution.
It is possible for me to agree and disagree with you at the same time. I am just not sure there is a black and white answer to this problem. The OP is going to have to figure out a solution for him.