Previously, Apple only had iTunes web previews enabled for iOS and Mac OS X apps, making it very difficult for users of the fourth-generation Apple TV to share their favorite apps on the web as well as for developers to promote their apps on their websites and social media accounts.
Although the feature is still rolling out, it appears it's limited to tvOS-only apps thus far. Kevin MacLeod of AfterPad told MacStories "that while the iTunes API is now returning screenshot metadata for tvOS-only apps, that metadata is absent for iOS apps with tvOS support."
Two of the first apps to feature web previews are currently Disney Infinity 3.0 and Beergeek.com TV. While these previews offer users and developers a way to see what an Apple TV app looks like or what features it has, they do not include any way for users to take any action.