Looking at the existence of caches in our CPUs and computers (and all CDNs), I conclude that the 80/20 rule apply to dish washing!

(/s)

But really, it might just be that people use 20% of their dish-washable objects 80% of the time. So having 2 dish washers eliminate 80% of the labor of putting them in the cupboard because 80% will be gone in the other machine by the time you really have to fill the cupboards.

Then again, that's lazyness and I suspect the higher humidity of the dishwasher is an health issue.

No, in fact they had two self-cleaning cupboards.

Hell we've only ever had at most one dishwasher, and Mrs Funk is always treating the bloody thing like a cupboard.