I have seen scarf welded tangs on many blades from many cultures...Indian,Persian,Chinese,some Japanese knives and tools,and various european blades.
One can argue it is conservation of some materials or some requirement of function.
To determine if it is a functional mechanical requirement we would have to sample the two bits and see if there is indeed a difference...chemically as well as metallurgically.
To my knowledge none have done this type of study.
As far as needing iron in the tang vs steel...one could always just not harden the steel tang and thus have very similar pearlitic properties in the steel as one would find in ferritic iron.
I think a point could be made that the steel in the tang could make another small knife..so why not make another small knife? A forge weld is not a difficult thing to do...takes only minutes once you have the tools and skills.
Ric
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