Well, as it turns out, some of these gadgets are linked through affiliate links. Here's the source code for an Overstock gadget http://myzytu.googlepages.com/overstock.xml
And here's the source code for an Ebay gadget from the same person. http://myzytu.googlepages.com/ebay.xml
I can't imagine that Google approves this but I can't find where it is prohibited in their T&Cs.
It does violate Linkshare's and CJ
's T&Cs since he is offering his gadget to be published on sites that he does not own.