What's really interesting about this business model is not the fact that you can buy a car online, it's the price transparency that you create with this: Car dealers often have 10-20 % margin on a car sale, and they make most of their money by providing services to you after you bought the car, so they are usually able to give you some big discounts. Also, as they usually receive a bonus by the car maker for selling…
You should never pay more than invoice for a new car. For that matter you should never buy a new car, it doesn't make economic sense.
It probably also makes no economic sense to shop at Macys rather than Goodwill or to buy a house rather than a shack. People pay more for things they want.