Car companies advertise horsepower as desirable because it lets you go fast, but perhaps more importantly, the American Model encourages you to slow down any time you feel it's advisable, because you can get back up to speed quickly and cheaply.
In contrast, the Rest of the World Model of expensive fuel and small engines encourages you to conserve your velocity, because it's time consuming and expensive in gas to get back up to speed after you slow down. So, you really don't want to slow down until you get to where you're going, no matter how many ladies are pushing baby carriages across the road in front of you.
Also, the American Model means there are much smaller class differences on American roads than on Rest of the World roads. The differences between high end and low end cars on American highways aren't that salient. They can all go 75 mph and can all accelerate more or less adequately. In the RotW, however, the difference between the 0-60 in 14 seconds subcompact you rented and the BMW 7-Series bearing down on you from behind at 100 mph is not immaterial. Not at all.