Maybe it's nothing more than keeping their reviewers busy. I don't agree with the notion that they are doing this to preclude competition from doing something else with Flickr images, unless it's to preclude Flickr itself from getting into micro stock. I can't see, say, Yay, having to prospect through so much trash to find the marketable ones.

__________________
istockPhoto
Shutterstock
Dreamstime
Stockxpert
SnapVillage
Fotolia
BigStockP
FeaturePics
YayMicro
TheNextMicroWannaBe