David:
Nobody is arguing that older equipment is not useful. As for the choice of words, "dead system" means perhaps different things to different people. To me (and likely Guy too) it means a system that no longer has OEM support for repair, replacement or newly introduced *and compatible* bodies, lenses and accessories.
I do own lenses for my Leica M's for example that are no longer made. HOWEVER, if one of those lenses fails and cannot be repaired, I can still buy brand new lenses of the same focal length from the same manufacturer -- OR even choose from several third party manufacturers -- to replace them. Thus this system does not present a "dead-end" to me.
In the case of the Contax 645, a user is relegated to a predominantly used and relatively limited market; there were not many (any?) third party offerings I know of for the Contax 645. (Yes, Hassy lenses can be used in stop-down mode via adapter, but no AF options I know of?) So while a continued supply of working bodies and working lenses is certainly available, nobody can say how long it will last; it will last as long as the stuff that's out there works or can be repaired, and when that used supply is gone, then it's done...
Similar is the Hassy V system. The big difference however is Hassy V has been around for many, many years, and hence there are a plethora of used bodies, lenses and parts still available -- AND a bunch of third-party choices. I do not have any idea how large the used supply of Hassy V is, but certainly considerably more than for the Contax 645 AF. So while it is also close to being a "dead system" it is unlikely a user will run out of replacement parts anytime in the foreseeable future.
In my own MF system, Mamiya, I would say that any of the pre-AF Mamiya 645 bodies and lenses are part of a "dead" system. Yes, the older lenses can be used on the current bodies, but none of the current lenses or accessories can be used on the old bodies. As soon as the supply of compatible used bodies dries up and can no longer be repaired, it's done too.
One final point: Very often a working pro looks to viable and rapid replacement or replenishment of their gear. Should one of my lenses or my body fail and I have a job to use it on tomorrow, I need to be able to get my hands on that replacement right now today, not next week. I can go to any number of camera stores and rental centers in most any major city anywhere in the WORLD, and find replacement gear if needed. That is what it means to me to be using a supported system.
Hope this helps explain my view better!
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