They are equally easy to stop (simply standing in the road works just as well) and are even easier to take control of (one can always put a gun to driver's head and ask him to hand over the keys - thieves won't be able to pull this trick on a robot).
Experience will tell him how much to slow down, whether to swerve around the obstacle, edge past slowly or stop altogether. All the time he'll be making judgements based on the appearance of the person, the surroundings, etc.
If the person seems malicious he knows just how fast to drive to intimidate them into getting out of the way, without undue risk. He doesn't want to kill anyone, even if they're trying to rob him.
Now imagine encoding all of that into an algorithm. I'm not saying it's impossible, but it's a huge challenge.
Also bear in mind that autonomous vehicles will probably err very much on the side of caution when it comes to pedestrian safety.