The difference is that Gill just banged out a statue, stuck it on a building and walked away- after which it persisted as a discrete and separate object- whereas Jackson- the person or persona- is everywhere present in his art. That's his voice singing and his legs dancing. When he protects the kids from the evil drug peddler in the movie Moonwalker we now know it wasn't exactly like that and when he pleads to be left alone we know the reason why. A performing artist is much harder to separate from his art than a sculptor or a painter or a composer. Does a Jackson song performed by anyone else amount to much? Can it stand alone? Does it have a life apart from his?