I won't speak to the quality of art on the Amazon site as I browsed rather shallowly and don't have anything nice to say. Rather I will comment on the presentation.
This is certainly a time when Amazon's one size fits all store presentation falls flat. There is a whole field of expertise involving the presentation of art, and they haven't done a great job of making it look appealing.
Then again, maybe it's appropriate that a search for Warhol paintings share a layout with a search for Campbell's soup:
Warhol: http://www.amazon.com/s/ref=nb_sb_noss?url=node%3D6685299011...
Soup: http://www.amazon.com/s/ref=sr_hi_4?rh=n%3A16310101%2Cn%3A64...
Edit: adding a link to Arsty for those who are unfamiliar.