The short answers are: cars can be resold, so you're only paying for interest, taxes, depreciation, maintenance, repairs, insurance, and gas.
After working with vehicle data for 6 years, I can guarantee that someone who buys a 1-year-old Prius is actually paying less per month than you are for your 2005 Focus.
People who buy brand new cars are obviously paying a huge "drive it off the lot" tax in the form of depreciation, but they know that and think it's worth it. Some people are afraid to buy used, some like to drive a new car.
It's just another example of "it's expensive to be poor". If you can buy a better car, you end up paying less over the course of your owning it.
Of course, that idea breaks down if you buy something unreliable AND expensive. It also becomes fuzzier with luxury cars, since they're expensive to repair.
But a used, super-reliable car that holds value well, like a Prius or a Camry, is generally going to have the lowest total cost of ownership out of the whole spectrum of car options.