Why does my Time Warner IP address change depending on device?

Okay, I got an answer from a Time Warner rep on the DSL Reports forums. Basically, TWC does look at the Mac address of the device that connects, but they don't care what type of device it is. The IP is leased to a MAC Address for approximately 72 hours.

My AirPort router had been given the range 24.193.xxx.xxx address based on it's MAC.

When I plugged in my MacBook TWC saw a new MAC address and assigned it a 72.227.xxx.xxx range IP because it was available in the IP pool owned by TWC.

When I switched back to the AirPort, TWC saw its MAC and said "Oh Hai! You're back!" and gave me the 24.193.xxx.xxx address again because it had not been released yet.

I unplugged the AirPort for a few days and then plugged it back in and got a 72.227.xxx.xxx range IP.

Who knows why they do it but they can determine what device you are plugging in (or have a reasonable guess at least) by the MAC address which does trace back to a hardware manufacturer/maker and certainly assign an IP address based off that.

It would be interesting to see what happens if you plugged a Linksys router in.