The new Random House UK premium eBooks offer extras not included in their print iterations. These “ePub premium” files are created with extra content from the author:
Book and Beyond premium ebooks are a selection of titles from Random House that contain extra material, which can be video, audio, a quiz or just extra text. The extra content is designed to be used with Adobe® Digital Editions on a computer, as they require extra processing power to display! The extra content cannot be used on the Sony Reader or other hand held devices, as they do not have the capability to display the material.
The prices are pretty high (one title is listed at 23 pounds) and as noted above, they are designed for computer screens rather than phones or eReaders. Right now, they are available for purchase only in the UK.