Here's my (predictably) sociological take on this: what is or is not a work of art at a given point in time is a product of social negotiation, contestation, and consensus. There is no "essence" of art that shines through so people in every social context would define product X as art (in fact, the idea of "art" itself is culturally bound!). Put simply, X is art if there is a social recognition and validation of the work as "art": e.g., the producer of the work is respected as an artist, critics discuss the work, people pay money for the work, it is analyzed in art history classes, and so on. The platonic question "What is art?" is exactly the wrong question to ask here.
[WS:] Yes, to a point. But not everything is "socially constructed." There is objective material reality that makes some social creations last and other fall like a house of cards. One cannot just make things up and make them stick (either individually or collectively), one is always bounded by material reality. This is as Marxist as it gets, I believe.
This is also where the element of human ability to transform and manipulate material reality comes into play. It is called labor. Skilled labor is thus an essential and universal feature of art. Again, this is as Marxist as it gets. A belief that creativity is the ability to make thing sup out thin air, by the sheer power of one's will and imagination, seems to me like idealist anti-thesis of Marxist materialism.
I am not an expert on comparative art, but my cursory observations of what passes for art in various societies suggest that while the contents of what is considered "art" in these societies vary, there is at least one common element in them - namely that all of them required skilled labor, or craftsmanship, to create them. That craftsmanship may be possessed by a few or by many - which is the function of specialization, division of labor, and perhaps the social organization based on that division - but that craftsmanship seems to be a necessary condition of art, whether it is common or uncommon. Whether one is carving a ritual mask or a wooden figurine, or painting the Sistine Chapel - one does not do whatever, call it art, and make the label stick. Au contraire, one uses a specific skill that makes it art.
The fact that many people in one society have the wood carving skills needed to make a mask or a figurine, but few in another society have the skill needed to paint the Sistine Chapel is largely irrelevant here. It merely testifies to the existence of social conventions that allow certain people have certain skills and deny those skills to other - again something that Marx addressed quite explicitly. But these differences in the division of skilled labor does not mean that the skill to produce something of value is arbitrary and socially constructed. Our society may not put much value on carved wooden figures, for example, but the fact that such figures are of relatively little value in the US (Ten Thousand Villages or Marshall's sell them for less than what Nairobi merchants charge for them), does not mean that it does not take skilled labor to make them.
Wojtek