It's interesting how "what is art?" has become such a common question. There really is so much out there, but it does seem to have become a rather "cliquey" affair. Personally I feel monetary value is the worst yardstick for measuring the true value of art. Modern art especially seems centered more around eccentricity and shock value than around any kind of skill.
I once remarked to a highschool art-class classmate that went on to study art at varsity, that the art-world seems to have become an "industry" very similar to the music industry, where there are a lot of fakers and "industry manufactured" artists, with only a few great talents sprinkled inbetween. In many cases an artist gains noteriety only because one of the movers & shakers of the industry took a shine to them. Other times it's pure novelty, where the artist's background or peculiar style (or age) plays more of a role than any kind of skill.
I used to think that it was about conveying emotion, which should be easy for a master of any craft. Whatever the emotion might be, having the skill to create something that induces a similar feeling in others is what defines an artist. And the method used should be a question of which medium and style would best accomplish that.
It's like a story I heard about Abdullah Ibrahim: he apparently said that only Jazz musicians are real musicians, to which someone else (the name escapes me) replied that he only thinks so because all he can do is Jazz. (I'm not entirely sure how much truth there is to that story. Muso's can be pretty mean. But it has a point though.)
Perhaps art is the same in that regard. I know some of my favourite artists, like Picasso, Dahli, and Bacon, were perfectly capable of producing a normal portrait/still-life in other mediums, they just chose to use a style that they felt best suited what they were trying to convey.
As for Brett Murray's "Spear", I thouht the concept was great, but there were probably better ways of executing it other than the slap-dash looking application of cartoonish genetalia where a loose belt buckle and open zipper (a-la Zapiro) woul have conveyed the message just as strongly. Hasty addition perhaps, or I'm just being unnecesarily critical. Either way, its noteriety alone has turned it into somewhat of an icon. You can't buy publicity like that...