I think the funny thing is that DRM just doesnt wortk. So far I can find any Bestseller as a pirate on the internet even though all of them probably had DRM in the first place. On the other hand at least the original Pottermore(with watermark) ebooks in German are not to be found yet because probably nobady knows where exactly there personal data is stored. When I searched it was easy to find the english Pottermore ebooks though piarated which I can only explain as for the reason that they are available at online libarys.
but anyways for me it seems like this watermark makes way more sense because people are actually afraid of uploading these books but also makes it easier for the people buying the books. all this apart from the fact that it takes me like 30 seconds to remove the DRM of a book which should proof the point that its pretty useless and just prevents my grandma to by an e-reader other than a kindel because everything else would just mean she would have to call me every time she wants a new book on her reader