EddieS.
You can still have a Dynamic IP even when it never appears to change. If you never rebooted your Cable Modem, or even if you did, you can still get the same IP again. It happens frequently. Also, If you have your own wireless router you will appear to always get the same IP address even though your Cable modem IP address may change because you are connecting through your router. The IP address you see when using the IPCONFIG command is the Router IP address, Not the DHCP IP from your cable modem.
I have a wireless router and my main PC always has the same IP, subnet and gateway addresses, IP always =192.168.0.100 which is the router default IP so it never changes and yours is probably similar like 192.168.0.???...nearly all router use the same or similar defaults.
...Rich