[vectorjohn]

"A teenager doesn't just "want a car." He wants that freedom that car gives him."

Precisely, and this is why owning the car isn't that important. This teenager presumably still has to pay for the car and fuel, or bug his parents for it. Paying for the (cheaper) self driving ride is no different.

[icedchai]

So why not call a cab? or take a bus?

It is different. If you're relying on someone (or something) else, waiting around, you're not "independent."

[vectorjohn]

Cabs are expensive, relatively slow, and busses are just slow and don't take you to your destination.

Really, this doesn't seem like much of a stretch.