It does seem they really do sell the accepted images, but I'm through with filtering my images for them, retouching them only for iStock, keeping track of what was accepted and what was not, reuploading the same files and hoping for a "better" (Colja-friendly) inspector and so on. I'll just dump in the images and if they get rejected because of those overfiltered reasons (whose I don't understand looked at from a wider perspective, 'cause I've seen files similar to mine sell extremely well on iStock already), I'll just reupload them again and again. It is true that stock agencies have slightly different customer bases, but they're mainly looking for similar images and if mine sell at Shutterstock, for example, I'm sure they would with no qualms sell at iStock as well. And I've proven right on more than one occasion when the image accepted only the second or third resubmittion attempt started selling more than any other one (still extremely slow, but still "solidly" compared to other accepted files).
I've said it already in an other thread, but they seem to accept only my worst files. By that I'm not implying that my creations are awesome, not at all, but at least they could widen the criteria to digital creations (and not accept only raw photos) and the likes: we all know they sell good (if even better) than unmodified photos.
p.s.: Sybille, this applies as much to my Photoshopped photos than it does to your superb fractals. They sell, they sell well, but iStock ignores their potential and kicks them out of the game anyways. And I'll never understand why.