There's a big time & unforeseen circumstances factor here. As a hypothetical example: Suppose a well-off 20-something male buys himself a sporty car like a Mustang or 350Z. Besides being at perhaps the one point in his life where he would be able to justify such a vehicle, he also has an ulterior motive: To pick up chicks.
Fast forward five years. His mission accomplished, he has himself a girl and has settled down with her. They are thinking about starting a family, buying a house, all that other stuff. The guy needs a car that has a useable backseat, four doors, easy on gas/payments/insurance... all-around, a very pragmatic car. Suddenly, the Mustang/350Z doesn't seem like such a great vehicular choice, does it?
On a personal level: When I bought my Grand Marquis back in March of '05, I had no idea that I would need to drive 135 kilometers (84 miles) today in May of '06. Needless to say, the cost of fuel commands a signifigant portion of my budget these days, and I'm looking to rid myself of the gas-guzzling Mercury ASAP.
I'd like to say that, when the opportunity arrives for me to buy a brand new/much newer vehicle, I would drive it into the ground. So far, though, I haven't gotten that chance. And who knows what the future holds? What if I am "forced" to dump my car again, like I am with the Mercury? At this stage in my life, I cannot fathom having the kind of disposable income to dump a car just because I was "bored" of it. What if I have that kind of money to throw around later in my life? Will my opinion change? There's just too many variables right now.