Interestingly, I contend that the prevelance of 45 degree angles is in large part due to the capabilities of ECAD software. If you look at old manually-routed PCBs, 45 degree bends are rare. If you try to make a design with non-45 degree bends in most ECAD software, prepare for pain as much of the features of the layout engine fail to work properly (I had experience of this after being inspired by some images of TopoR-designed boards).
