Ignoring the laughable notion that Overstock is a thing, there’s a good question here- Overstock has an iOS app. If that app were to allow payment for orders via Bitcoin, would Apple ban the app? Where’s the line? Are retailers allowed to accept Bitcoin on their iOS (and assuming Google takes a similar stance, Android) app?
This is always the problem with the “walled garden” app model. Comixology can sell me the comic Sex Criminals on the web, and I can read it on the iOS app. But because Apple thinks sex is tabu, I can’t buy it directly on the iOS app.