As another article said about Hotz and Tesla's automated driving to make it 99% accurate is easy to make it 99.9999% accurate is much harder and these systems need to be that accurate. Also cars just stopping even 1% of the time would clog up every highway. There's an easy 200 cars going by at any time and if 2 are always stopped thats problems. But you're just pulling these numbers out of the air, don't think you mean 1% is ok. Further cars stopping in the middle of the road is not safe. If the error is on the person we can blame thats one thing but if the error is on the product that's endless litigation.
For riderless bikes not sure what the new thing is but certainly seems unnecesary and would have all the same problems as cars. As for the statistics driverless cars have not been out in any significant usage to determine if they are safer or not. Controlled studies with engineers babysitting them aren't representative.