I would bet that Google wants all your images so they can use image search to make money. First the regular search results got filled up with ads, the Froogle went from a free product search to charging by the click.
Image search is big on Google and has yet to be monetized. Google is also an investor in Zazzle. With all the images they could attract and a financial interest in Zazzle could they be prepping to find some way to create a back end to hook all those images into Zazzle (or maybe some other site) and 6-12 months down the road send out an email to all participants that says hey, want to make money selling all those images you uploaded, click here to opt in to our licensing and merchandising programs.
Rev share would probably be 70-30 in favor of the images owners, stock sites take a direct hit, pods take a direct hit and Google fills its image search with images you can buy through Google since Google would now get a cut.