The preponderance of stop signs on US roads is one of the most infuriating parts about American road engineering. (Along with such a large number of signs that it is not humanly possible to process them all when traveling at vehicle speeds.)
It really does condition drivers to look for signs instead of other people. If you run a stop sign, you'll get fined even if nothing happens. If you stop at a stop sign and then in blissful ignorance ram someone who didn't, no harm comes to you (unlike to the other person).
The book "Traffic" by Tom Vanderbilt is an interesting read about some counterintuitive things about how traffic works and about how differently engineers in different countries approach safety. I can highly recommend it.
EDIT: One of the most fascinating stories in the book is about how they redesigned some big 5-way intersection with a traffic light in some central square of a Dutch city by just removing everything and leaving a big empty square with some lines painted indicating the roundabout. Crashes went down, and traffic flow improved, because drivers were forced to pay attention to figure out how the whole thing worked.
Experience seems to indicate that the "safety" measures usually taken in the US (widening roads, removing pedestrians, etc) are totally counterproductive because they send subconscious signals to the drivers that this is a speedway which causes everyone to drive faster and pay less attention, which makes crashes more severe (not to mention relegates pedestrians, bicycles and other alternative means of transport to second-hand status.)