There is always a lag between price signals and infrastructure changes. With cars, it takes about 20 years to renew the fleet although strong pressures like gas prices can accelerate that.
Actually, you should read that too:
http://www.greencarcongress.com/2008/02/median-vehicle.html
What's interesting in the US is that both the median age of the fleet and the scrappage rate are going up. What it suggests is that recent vehicles are going to the scrapyard - cars sold during the gas guzzling madness of the past 10 years - but older vehicles, which tended to be pretty sober, are staying in the fleet. It would actually match a bit what I see around me, with friends churning through new fancy cars but also hanging dearly on their old Honda Civic 1989 for commute. So, I wouldn't be surprised if we see a reduction of a couple of percents a year in the US. Just because of market inelasticity, it could end up moving oil prices quite a bit.
But at short term, I agree. Demand destruction will mostly happen on the margins, in weaker economies where energy is a much bigger share of income, hence much more sensitive. It's already happening in countries that cannot sustain subsidies against current prices - Nepal, Africa, etc.
What it suggests is that recent vehicles are going to the scrapyard - cars sold during the gas guzzling madness of the past 10 years - but older vehicles, which tended to be pretty sober, are staying in the fleet.
