IP numbers belong to the IP stack and have nothing to do with interfaces. This idea is completely useless, forget it, this will make things (eg. routing) a lot more understandable. From this point of view, Jasons posting is IMHO very clear.
I only point it out because not everyone knows that there's a difference, and may think that the non-NIC interfaces are immune. I remember setting up my first ipchains firewall and thinking it odd that I needed explicit rules for the loopback interface, but it makes perfect sense in hindsight.
