In my slab the rebar was laid on 12" or 18" centers running vertical and horizontal, the main beams where 24" deep. I have seen beams 3' deep..
Some contractors in San Antonio do not use rebar, they use cables to hold the slab together. I do not think this is a trade secret but a large retail store does not have any steel in there slabs. They put steel in there outside beams and of course in the concrete holding up the columns.

The more you spread out the weight the less pressure on the slab.