'Themed Chess Sets' -or- 'Theme Chess Sets'?

I chose Themed Chess Sets, and have wondered ever since if it's correct. Google prefers 'theme' to 'themed' by almost four to one, so I'm in the minority. My examples -- Historical Themes, Animal Themes, Children's Themes, and Sport Themes -- all lead to an About.com adaptation of PriceGrabber.com, where any proceeds go to persons unknown. I might change that some day to use a bona fide chess supplier, but for now it will have to do. In the meantime, add another converted article to Been There, Done That.