The issue of weight is easily resolved when you consider the weight of the saddle + luggage system for commuting, long day rides and light weekend tours.
With a B17 you can strap on a Carradice saddlebag for 7-25l of easy to carry, aerodynamic and durable luggage.
With a lightweight racing saddle, most people would opt for a seatpost clamp rack with a rack-top bag. This is heavier, weaker and less aerodynamic.