I know the FFS was offered in '82 along with the Selecta crankset and I have seen a road bike fitted with these and a conventional derailer set up... another friend rides a townie much like the Suburban with the one piece crank that does have the skip tooth cog on the freewheel and conventional friction shifters.

I think the differences came down to who was doing the building and the price point they were aiming for...the Positron was a unproven and new concept for many and believe it was a pricey option compared to conventional friction shifters.