Virtual Server via NAT

My wirless broadband router, model Planet BLW-04EM can support Virtual Server. That is to say, the WAN interface can pass Internet traffic to an internal host 192.168.1.x as if the services residing in 192.168.1.X are on the Internet. I have started IIS and access the WAN real IP address can redirect to my default web page through the internal network. That is to say, the Virtual Server is up and working satisfcatorily. However, if I try to access http:// followed by the WAN IP address from other hosts on the Internet, nothing can be seen. I believe my ISP has barred inbound traffic to port 80 of client IP addresses. Just wonder what good it is to ban port 80 inbound traffic ....