I had an air-cooled Vanagon for a while. It was 2½ tons, due to aftermarket camper modifications, and could manage a bit over 60mph on its 70-horsepower 2-liter air-cooled engine, despite having the aerodynamics of a brick. Something with half the frontal surface area or half the drag coefficient, such as basically any modern vehicle, could manage quite well with half that horsepower.
I think the average US car weighed a lot more in the 1960s than in the 1970s, 1980s, or 1990s. Maybe widespread SUV use is pushing that average back up.
Reading the content of the article you linked, the first version had 9hp and was "notoriously underpowered". Most 2CVs actually came with engines around 30 HP. This car also weighed only 560kg, which is lighter than even a Smart Fortwo. Modern crash safety standards mean it's effectively impossible[0] to produce street legal cars that weigh less.
The fact that a car was once successfully sold in Europe with such a low power to weight ratio doesn't mean it would succeed in today's market. Consumer expectations have changed. They could change again, but there would have to be a good reason.
[0] Lighter cars could be made from more exotic materials, but those would drive the price out of reach of the average buyer.
I think the average US car weighed a lot more in the 1960s than in the 1970s, 1980s, or 1990s. Maybe widespread SUV use is pushing that average back up.
Did the http://en.wikipedia.org/wiki/Deux_Chevaux really have only two horsepower?