Morendil, my guess is that you don't question whether having a car is the "normal" choice, either, but you have started to question whether it's the efficient choice. Most people don't evaluate the economic efficiency of owning a car precisely because everyone agrees that it's normal to own a car, and people often just do what they see as normal without stopping to think about it.

Incidentally, zipcar.com, an hourly car rental service, sometimes runs ads that break down the cost of using a Zipcar for your driving needs on an annual basis vs. the cost of owning a car. I checked the math on one of those ads and found it persuasive; I've been using Zipcar for 3 years now and have never felt the need to own a car.