the "rod adjuster" you are referring to is part of the slant-parallelogram mechanism that enables the derailleur cage to move in parallel with the freewheel during shifting. Campagnolo calls it the "Twin-Axle System". you can read more about it at http://www.equusbicycle.com/bike/campagnolo/crocedaune/crocedaunebrochure%203.pdf.
incidentally, Japanese maker Suntour also incorporated a similar slant-parallelogram mechanism in their fantastic Superbe rear derailleur back in the mid-80s.
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