I've had quite a few routers in the different places, ISPs and configurations I've had over the years, most home-based routers are simple, too unsophisticated to deny you to access addresses, but allow others on the same network to those sites.
So the question then is "how could you do this?"
The static IP address gives one possibility; because if you have a static IP, you have to also set the DNS server. He could be running a DNS server and that server is configured to not resolve specific sites. This would require the least special setup in that the DHCP server is turned off at the router (it's not acting as a DHCP server) and the DNS forward could be disabled.
How would you test this? Is your default gateway the same as your DNS server's address when you run "ipconfig /all" at the command prompt? If not, then this scenario is likely.
Problem with this form of restriction, it is easily circumvented, by changing your DNS server's address to (say, your ISP's) you've bypassed his restricted DNS server.
The other way to do this requires far more setup, but is much more difficult to break. The wireless router would be connected to a PC and that would have another network interface connected to the cablemodem/DSL modem. This would not be an out-of-the-box setup, I can do it (and have done it) with a Linux server using iptables and squid, Windows would require a third party routing software capable of redirecting outbound traffic based on the destination port and a filtering proxy.