I was scanning the web and I noticed this:

In reality, it’s not that hard to get better mileage: drive slower, reduce weight, and increase aerodynamics. None of this seems to particularly interest Detroit, since better mileage tends to increase the amount of time people own their cars before upgrading.

This is the stuff that tweeks the interest of the Freakonomics people myself included. This of course it terribly interesting to the marketing/economics people at automobile companies, after all it is not in their interest to have new cars with a lifecycle beyond three years, but it also explains a lot.

Perhaps people with smaller vehicles travel less hence are less likely to change their vehicles regularly, or they are simply less inclined to view a vehicle personally, but rather as simply a tool, much like a microwave. I dont replace a microwave after 3 years regardless, I replace it when it collapses.