Running in the street

I wonder why it is that a good portion of the people I see jogging, do it in the bike path beside the road instead of on the sidewalk. When I'm walking somewhere (or in a parking lot) I usually like to keep something between me and the cars going by. A curb would work great I think since if they aren't paying attention and they're "coming right for me" they would bump over it and hopefully that would draw their attention back to their driving (or lack thereof).

But so often I see people jogging (against traffic usually, which implies they're not totally insane) on the side of the road instead. Both are paved surfaces so it's not like one will be easier on the feet. You can do side by side running if there are two (or more) of you but that puts somebody even further out there in the no-mans land that our roads are today.

So what's up?