Here is a post from a Kobo developer outlining their experience with their store. It doesn't sound like there was any room for taking a stand in their case and that they got boxed into not being able to communicate anything about their product. It does sound like there may be a different set of rules for different apps enforced capriciously but I doubt it had much about Amazon taking a stand.

http://quatermain.tumblr.com/post/8045895465/my-review-of-th...