In most museums you CAN take pictures. In places where you can't its not because you might try and sell a copy, its because on older paintings, many many flash bulbs over time can damage them. They've actually lessened that rule now that people can often take pictures without a flash, and some museums state "no flash photography". You can take pictures in the Smithsonian, for example, even in the galleries.
Anyway, that is a beautiful sculpture, but that artist is either being a jerk or he is doing it as a media stunt to get more attention for his piece (which is very common in contemporary art).
I mean, look at how people are reacting. They are taking LOTS of pictures and posting websites despite him. Wowie, free promotion. I don't thik that artist is as dumb as it seems at first.
As an afterthought:
Maybe the piece in itself is in part conceptual. Maybe it's about "who owns copyright in reflected images." I mean really. it wouldn't be ANYTHING the same if it was a matte material, would it?
I think there's a lot more to this than meets the eye, heh.