Whatever the actual reasons... I bet the official reason to the public will be something like:
We at Apple saw that being giving customers a choice to purchase the version appropriate to their lifestyle, we were able to accommodate a segment of the population with their specific needs. Needs that would further provide for a slightly greener earth. By not incorporating the 2 grams of copper wire and qi wireless charging technology in cases where they would not be used, we are able to reduce our carbon footprint that much more.