I don't see what's so great about these artists.
Some individual works, yes. But not the bulk of their work.
The monetary value of a photo or other artwork has no correlation with its aesthetic value. A badly-composed childhood mugshot of Hitler would be worth a lot. Rembrandt could have taken a crap on a canvas, smeared it around and it'd now be worth millions.
Instead of talking about hypothetical crap canvases, let's talk about something that really exists:
Are these cave paintings of any intrinsic value, or are they just random doodleings that could have been made by any 6 year old? I would argue that they are of immense historical AND artistic value, simply because they represent some of the first attempts at pictorial representation of the world at large. It doesn't matter that you or I could do better drawings (well, not me...I can't draw AT ALL!); the paintings have value because of what they are and - GASP! - who made them.
Consider this photograph:
Is this a valuable photograph? Of course; it's the first one ever taken.
What about this:
The latter photo could have been taken by anyone and posted on Flickr. But why is it good? Just because it was taken by Andre Kertesz?
This is far too broad a discussion to have on an Internet forum, to be honest.