Originally Posted by damian_
My guess is proper bike shoes tend to have stiffer soles. Riding in normal athletic shoes puts pressure on a small area of my foot, whereas bike shoes distribute the pressure across your entire foot.
I would agree that it's the shoes that are probably at fault rather than the cages. In addition to the above mentioned pressure distribution I've heard that the minute flexing of the foot around the pedal platform contributes to numbness, and obviously a stiffer sole will reduce that phenomenon.