I think what the poster who included those pictures was saying was that these stars were obviously not anti-consumerist. But he was being ironic, and I think trying to make his point through snot as opposed to argument. Maybe by the photos what he meant to say was that since these stars are obviously steeped in consumerism, then the statement that many artists tend to be anti-consumerist is false and laughable. An similar line of argument would be:
Person A: "Most football teams play only 16 games in any given season." (a statement analogous to one like "Most artists take anti-consumerist stances")
Person B: "But look at this picture of the Denver Broncos, the SF 49ers, and the Seattle Seahawks. They're football teams, and they made it to the playoffs last year and played more than 16! Boy are you stupid!" (a statement analogous to the one being made in the posting of pictures of Madonna and friends, i.e. an attempt to disprove a qualified general statement by finding an exception.)
Other possibilities: 1). These are the people that the poster considers artists, and represent his taste for music and social commentary. 2). He's just joking light-heartedly and I'm misunderstanding him. 3). The pictured people really are artists, and their exaggerated embrace of consumerism and materialism is a statement of it's own kind.
Then again, the whole thing just proves my point that it's impossible to argue these things on this CCJ forum (read above posts to decode that one).