I remember when I used to play Diablo II that I often find a socketed Wirt's Leg when obtaining it from Tristram. Could you make a rune word out of it? Or was it just socketed sometimes because it was considered a weapon? I'd find it out for myself, but I don't have the game anymore at the moment.
I only remember picking up a single socket Wirt's Leg. It may be that you are only able to pick up a Wirt's Leg with 1 socket, making it impossible to create a rune word. It may be that the developers have removed the ability for rune words to 'activate' on the item. Since one of the requirements in activating runewords is its application on a specific weapon, I would say it is the later.
It is no longer possible to make a runeword in Wirt's Leg. Wirt's Leg does drop in socketed versions (1, 2 or 3 sockets possible.) In earlier versions (1.09, perhaps just 1.07) it was possible to make a runeword in Wirts Leg but not in the current version.