Well, lo
is a loopback device that doesn't have a hardware-relatable state, whereas eth0
does.
superuser@hermes:~$ ip link show up 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 link/ether 0a:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff