Possible answers:
- Premium seats booked with mileage are capacity-controlled and would likely go empty anyway. Thus, the supply and demand principle dictates a lower price in miles.
- People paying cash for seats in premium cabins are not as cost sensitive as those paying miles for the same seats. Revenue C and F are generally purchased by business travelers, whose expenses are paid for by their employers. Businesses generally do not have a stash of miles with which to purchase their employees' tickets; thus, mileage C and F are generally purchased by leisure travelers. Leisure travelers generally cannot afford to spend 400% more than the price of a Y seat for a C seat. Thus, the principle of cost discrimination dictates a higher cash price.
Any better answers?
I think your answers are right on target.
I think an additional reason (that dovetails off your price discrimiantion point) is that if premium awards were priced in proporation to the "cash" price of the ticket, very few customers would have sufficient mileage to redeem such awards.
Not sure if this reason holds up, but I also think encouraging redemption of FF miles for F/C allows product "trial".
Extending off your point, the price differnetial between F/C/Y on RTW tickets is far less than point to point tickets. Goes right back to price sensitivity, as RTW tickets aren't convenient for most business travelers.