There are pedestrians and vehicles. I would guess WD's Chicago is bigger than SS's Seattle and the density of pedestrians and vehicles is higher in WD.This has probably already been covered, but doesn't Watch_Dogs have people walking around in the city? Infamous has no pedestrians or vehicles, though, right? (Admittedly I don't know that much about Infamous: Second Son, and I do think its graphics look amazingly impressive. I'm just wondering about this one particular point.)
Pedestrians flee when you start engaging in combat though, so if you only watched a little amount of footage that involved combat then it could look there are none.