Understood. I just figured that though it might not have been a typical factory option, anyone who wanted one would pick up whatever was available at the local bike store.

As I recall, when I got mine there was another option. Someone, possibly Shimano, made a generator which sat between the chainstays behind the BB and bore on the center of the tire tread. The guy at the bike store seemed to think it was a better arrangement but it looked like a great place for it to pick up road dirt.