Also, PageRank clearly doesn't need a patent. Google's done just fine against competitors that have ripped off their technique.

How do you do that?

The first person to think of the concept of "self-driving car" gets the patent? That will just lead to a flood of patents on things that don't exist yet -- basically a patent troll's dream.

Perhaps the first company to build a working prototype? What happens to all the other companies that almost have a working prototype -- do they now have to sit on the sidelines for 10 years?

How do you even know what a "working prototype" is in that scenario? Is it acceptable if it is just capable of driving on straight roads during sunny days with no other cars or people around?

I think patents on specific, narrow pieces can make sense: for example a laser-based 3D vision system, or a specific algorithm that identifies people about to walk in front of the car (even that is tough, because there's a thousands of very distinct approaches to that problem).

Patenting the entire system (the "self-driving car") makes about as much sense as say, Herman Miller patenting the concept of a wheeled office chair. They can patent elements of their lift mechanism, specific wheel designs, or arm adjustments, but not the concept of combining wheels and a place to sit.