I feel like I'm trolling this thread, but my reason is that I was really confused when the DW came out. I thought it was a stupid idea, but the more I thought, and analysed it, the more I think it's a great idea. So let's take it one thing at a time:
Weight: the configuration allows for a very light weight car for what it is. nocones was giving the example of a F1 car (642kg) and a formula Atlantic (560kg) as cars with similar weight. Both of those cars are open-wheel single seat cars built for pure speed. The DW in comparaison is a full-fendered "two-seater" built to survive a 24hr race. Would it be faster than a FA? No. But the fact that it's even close is extraordinary. With the "trike" configuration of the DW, you don't need a very torsionally stiff chassis which allows you to save weight.
Weight distribution: With all the weight concentrated at the rear, it helps with both the acceleration and braking of the car. The weight is right on top of the rear tires, and with it so close to the rear tires, there is very little weight transfer to the front wheels, which means the front brakes have a smaller portion of the work to do, allowing them to be smaller and lighter. The rear CG location also allows you to concentrate you downforce towards the rear.
Aerodynamics: This is the hard one to prove because L/D "lift/drag ratio" is not a constant between cars and it's not simple like saying more downforce=more drag. The only number I have is a drag coefficient of 0.35 for the DW. For an open cockpit race car (downforce or not), that is a VERY impressive number. For comparison, the AUDI LMP1 has a quoted drag coefficient of 0.47. And it's a close cockpit car, which makes a HUGE difference on drag.
About the LMP1's front wheels, it doesn't make much of a difference if the front is blunt or not. It's what you do with the air once you have split it. The bodywork behind the wheels, and it's interaction with the rest of the car is what is more telling. You will see that they are trying to detach the flow away from the back of the car.
But drag is very hard to understand because sometimes, it can be completly counter-intuitive, especially when turbulence is used to reduce total drag (like the dimples on a golf ball). And sometimes very little things can have a big effect. Like this classic NASA analysis shows:
Look here for the full story.
I'm done.
