Imagine you're driving along enjoying the day in your mediocre car when you come across a nice shiny new vehicle just sitting around with no one else in sight. You could jack it, but that is actually illegal in most societies as far as I'm aware. However, EA thinks otherwise.
In their new video for Need for Speed: Most Wanted titled Find it, Drive it, you could be driving around in an Aston Martin V12 Vantage and all of a sudden you come across a nice Mercedes SL65 just sitting around. You might be thinking about racing around in that Mercedes instead of your little Aston Martin. Well, you can actually jack a car that you see sitting around and use it for racing. The video only shows taking the Mercedes and racing with it (and then outrunning the cops afterwards), but since all cars are open from the start, if you find it, you can drive it.