The second thing they can do is have what is known as virtual hosts. That is you can run many websites with only one computer. So every time a hosting company signs up someone to use their equipment for having a web site, it is almost like free money as it does not cost them any additional money to host your site (unless their equipment is at full capacity). For example, we love to have virtual web hosting. You can set up websites for special purposes and be at their own special web address. For example, we are running all the following sites and more all on an old Intel now a Pentium III computer (on a private network).
Amazing is it not. What a cost savings and ROI (Return on investment). Before some web host wants to charge you an arm and a leg to host your site, ask them what you are really getting for your money.