East of where I live there's a relatively low population area where the roads are perfectly on the N/S, E/W grid. I wish they would use NW/SE, NE/SW instead, though. When you're driving east in the morning or west in the late afternoon, you end up looking straight at the sun.

I'm pretty confident most of them resulted from farm roads (probably following terrain as you mentioned) where meeting up "close enough" was fine when you had a dirt road and heavy traffic was two wagons. That turns into a clusterfrack if you expand into multiple lanes going each way and turn it into a controlled intersection.