Why are Apple's customers so passionate?

I saw an Apple logo on the car in front of me today and it got me thinking… How did Apple create such a loyal and passionate user base?

I’ve always owned PC’s, but have been very, very pleased with my iPhone for more than a year now. I’m a happy camper, but I’m not about to put an Apple sticker on my car.

Sure, their products are often very good. But so are a lot of company’s. What do you think causes people to do the company’s marketing for them?