All that's true. A good pair of driving lights (Cibie Super Oscar 10" or 8" Lucas "Flame Throwers") will totally light up BOTH lanes at a distance of 1/2 - 3/4 mile or more. That's a long way and a distance that few drivers, these days, would feel comfortable with, whether or not it's day light out. Most modern drivers are happy looking ahead to the next car, let alone the two or three ahead of them. Those guys would appreciate fog lights sweeping the road immediately ahead of them more than driving lights.
And as Dave pointed out, avoid the "Spotlight" version because they are unfocused and seem to light up half the World. Great in the desert at high speeds, very un-cool on the highway.
So to IM Bob's point, the absolute BEST setup would be a 4-light configuration with two fogs and two driving lights, two aimed out (Hi-Beam) and two aimed in close (Lo-Beam) that get automatically switched with the dimmer. I have the wiring for that on my Speedster, but felt that four Marshalls - or Marchals, if you're French 
- would look a little crowded out front.