What I'm seeing is the indications you get when you have a broadband router in the mix. Note that 192.168.xxx.xxx addresses are private LAN addresses. When I directly connect my cable modem to a PC, I get my real Internet IP address, not a private network address. I believe your modem is a standard DOCSIS compliant modem, so that behavior is odd to say the least.
You don't happen to have ICS configured, do you?