In the first case, the artist has made all the money they were going to get from the original sale, and the subsequent theft is that of their intellectual property.
I see your point, but that same point implies there was only one painting and the artist would have only made that single sale from it, as opposed to a Second Life creator who would make multiple future sales from an item.
It is equivalent of buying a painting at an art show, taking it home, making posters from the image, and selling them online.
