Consider who is likely to talk.  Someone says that they're not reducing their miles, so in answer to "Are you driving less due to recent high gas prices?" is either a simple, "No." and they keep walking, or a "No, and those #$!@#@!@#@@ gas companies should be !@#!#!#%@#$!# !  GM rules, Ford sucks" or something similar.  Then there are the people who are reducing their mileage, or doing something similar.  They're quite happy to go into length what they're doing, because people generally like to talk about changes that they're making in their life.  Thus, they give a good sound bite.

Another thing to consider is that people tend to see themselves as doing something better than they are.  Consider running about to do 3 errands in one trip when all errands are about 10 miles from one's home.  The car is still started 4 times, and a few miles are saved, but unless all three of those errands are in the same parking lot, or very close, not too much gas will be saved.

Additionally, behaviors might be the same, but just labeled differently.  If someone's running out to location A and they know they need something from location B, they will try to do it then to save their time.  The classic "harried housewife" is calculating how to best route her trips to take up the least time, and thus everything is getting condensed.  Now one is doing that, except they're doing it "to save on gas."  It's the same behavior, and the trips are the same, but their brains label it as something else.

And lastly, some people resolve to do something, but just don't end up doing it.  Just as some people are perpetually going to start knitting, learn painting, or some lofty goal which they like to say, but they never get around to it.  "I resolve to condense all my errands and just run them all once a week."  But you forget something, and you need it, and hey, if you need it, you need it, so just go out and get it.  No harm.  Oppps, I need something else, so let's go out and get it.  Oh, and X invited us to visit, so let's drive over and do that.  Everything adds up, and despite resolving to do less driving one still keeps driving.

Through mixtures of all of these, I think that is why it seems that a lot of people say that they're trying to save on gas, but results differ.  Additionally, go out to public message boards (which aren't specifically PO or enviromentally green oriented), and try and compare the number who say that they're trying to save with those who say that if they've got the money they're going to spend it however they damn well feel like it.  And try not to ask if they've actually got the money, or if they've got the loans/credit.

Consider longer commutes.  The wider the range for recruiting employees, the more likely they can get the best, most productive talent.  Conversely, if I were compelled to walk to work or use public transit, I'd have to settle for lower pay in a position where I couldn't use my best talents and for fewer hours a week.  Consider what happened when New Orleans restricted city jobs to city residents - the police department had to hire lower quality officers.

On the consumer side, big stores offer economies of scale and scope.  Autos make more of these in reach of more people, allowing both competition and selection, saving money over the non-auto range.

In both cases, one can get more done with one's time and money with an automobile, thanks to gasoline.  Time is the ultimate limiting factor of production.

The real corrolation is MORE driving makes for a BETTER economy.