Notice the small Diesel that's being offered on the F150 (3.0 liters). Why not a 3.5 or 4.0 liter so you can tow some serious weight. They don't want to step on the F250's toes and give people a more affordable option.
The ecodiesel is not being made to tow heavy, they are being made to get great fuel mileage. The RAM 1/2 ton is the only small diesel right now and it's getting all the market share. If I was doing a fleet of service trucks that would be my choice.
Even though new 1/2 ton trucks have a higher GVWR than older 3/4 tons you still need the right tool to tow heavy. I've occasionally towed a bobcat or a tow behind crane lift with my V8 F-150 - but If you have a 5th wheel full of horses to haul or a 35ft camper on the interstate you better have the money for a proper truck to haul it.