I see what you guys are saying as I have both posted a skin and been guilty of posting artwork without the skin.
By way of a solution, what about setting up a thread in the form of a gallery. Those who want to simply show off their talent may post images to the gallery, whilst those who wish to provide skins for the collectors can add to the regular threads.
I don't have the know-how to do this, but if someone who does thinks this idea makes sense, perhaps you could have a go.