IANAL but I'd assume it is hard to argue that there is a common expectation of profit when purchasing art, even though this is why some people buy art. Furthermore, the profits you would make upon reselling the piece of art are not coming solely from the artist's efforts. The artist got paid for their efforts and your profits are coming from your ability to market the piece and negotiate a better deal. In other words, you have some control over how much profits you gain and the artist is out of the picture (ie. they are no longer spending effort to help you make profit).

But a securities law expert would have a better explanation