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I think the paraphrasing you posted is ignoring the fact that the favorable pressure at the front of the vehicle is exerting a rearward force. That's what drag is all about-- the surrounding air exerting rearward force on the vehicle. That's why turbulence creates drag, that's why the vacuum at the back of a vehicle creates drag.
Otherwise, how do you explain the Prius's front end? Why didn't they use more traditional looking front bodywork? The article I posted shows diagrams of different nose shapes, and they quantify the effects of noses, hood angles, and windshield angles on drag.
BTW, it's not exactly momentum I was talking about... It's the fact that it takes energy to push aside fluid when you're surrounded by the fluid. The vehicle has to compress a large volume of air. Look at the smoke lines from a wind tunnel-- a lot of air has to be displaced, and of course displacing it more slowly by using gradually sloped surfaces costs less energy. Frank Lee said earlier in the thread that the air molecules are trying to get back to where they were. Well they don't remember where they were, they're just being pushed back into the area behind the vehicle by the higher pressure surrounding air.
Just like the gradual slope at the front makes displacing air cost less energy, the gradual slope of a boat tail makes replacing that air cost less energy and so it's easier for the atmosphere to push those molecules back into place.
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