Hmm. Perhaps. Personally, I've never noticed this.
Anyway, the concrete example doesn't matter.
I guess you know what I was trying to say: implicit communication between humans. Even without eye contact, there will be a host of minuscule actions (or inactions) that we use to convey intent. There will always be humans on roads, e.g. as pedestrians. Vehicles will be forced to interact with them, and this communication barrier makes it very difficult.
Don't think of highways, think of supermarket parking lots.
But I get your point.
People compensate by being very careful when parking and of course you can always roll down your window if the situation requires it.
A robotic vechile simply couldn't manage here. There are way too many dynamic human exceptions. For example, it's common to drive against traffic on the wrong side of the road for short distances since the intersections are so far apart.
However, one thing that I haven't seen discussed anywhere, but that strikes me as a hard problem: by having a non-human driver, you're literally taking out the human element of communication.
Everybody is taught about the importance of eye contact in driver's ed. What will we replace it with? I have no clue, and I doubt anyone else does. Yet it's a crucial technique we all use to negotiate traffic every day, regardless of our mode of transportation.
This is a hard problem, and it's less technical than cultural. It will be a bitch to solve.