Don't know about 20¢ on the dollar Peter ... 50¢ on the dollar is bad enough when we're talking $30. to $15K at rocket sled speed. ... but point well taken. I pity those that buy new and can't write it off ... big difference between business and pleasure ... depreciation softens the blow.
I also think that other innovations come into play depending on your end purpose. For me, it was worth $3.5K more to go from the H3D-II/39 to the H4D/40 because of the True Focus and better high ISO performance when shooting candids hand-held on the fly. Otherwise what's the point? I passed on the H3D-II/50 meg over the H3D-II/39 meg because the camera was exactly the same.
NO ONE critiques their current gear because those looking to competitively justify their own choices will jump on it like a Black Bird on a June bug ... It's just human nature.